JP6283515B2 - Ionic liquid, lubricant and magnetic recording medium - Google Patents

Description

  The present invention relates to an ionic liquid composed of a Bronsted acid and a Bronsted base, a lubricant containing the ionic liquid, and a magnetic recording medium using the same.

  Conventionally, in thin film magnetic recording media, a lubricant is applied to the surface of the magnetic layer in order to reduce friction and wear between the magnetic head and the surface of the medium. The actual film thickness of the lubricant is at the molecular level in order to avoid adhesion such as stiction. Therefore, in thin film magnetic recording media, it is no exaggeration to say that the most important thing is the selection of a lubricant having excellent wear resistance under all circumstances.

  In the life of the magnetic recording medium, it is important that the lubricant be present on the surface of the medium without causing desorption, spin-off, chemical degradation, and the like. The presence of the lubricant on the medium surface becomes more difficult as the surface of the thin film magnetic recording medium becomes smoother. This is because the thin film magnetic recording medium does not have a lubricant replenishment capability unlike the coating type magnetic recording medium.

  In addition, if the adhesive force between the lubricant and the protective film on the magnetic layer surface is weak, the lubricant film thickness decreases during heating and sliding, which accelerates wear and requires a large amount of lubricant. It is said. A large amount of lubricant becomes a mobile lubricant and can have a function of replenishing the lost lubricant. However, the excess lubricant makes the film thickness of the lubricant larger than the surface roughness, causing problems related to adhesion, and in the fatal case, it becomes a stiction and causes drive failure. There is. These friction problems are not sufficiently solved by conventional perfluoropolyether (PFPE) -based lubricants.

  In particular, in a thin film magnetic recording medium having high surface smoothness, a new lubricant is molecularly designed and synthesized in order to eliminate these trade-offs. Many reports on the lubricity of PFPE have been submitted. Thus, the lubricant is very important in the magnetic recording medium.

  Table 1 shows the chemical structure of a typical PFPE lubricant.

  Z-DOL in Table 1 is one of commonly used lubricants for thin film magnetic recording media. In addition, Z-tetraol (ZTMD) is one in which a functional hydroxyl group is further introduced into the main chain of PFPE, and it has been reported that the reliability of the drive is improved while reducing the gap in the head media interface. There is a report that A20H suppresses decomposition of the PFPE main chain by Lewis acid or Lewis base and improves tribological properties. On the other hand, Mono has a report that the polymer main chain and the polar group are polynormalpropyloxy and amine, respectively, unlike the above-mentioned PFPE, and reduce the adhesion interaction in the near contact.

  However, common solid lubricants, which have a high melting point and are considered to be thermally stable, interfere with the electromagnetic conversion process, which is very sensitive, and wear due to wear powder scraped by the head on the traveling track. The characteristics deteriorate. As described above, the liquid lubricant has mobility such that the lubricant removed by abrasion by the head moves from the adjacent lubricant layer and is replenished. However, due to this mobility, especially at high temperatures, the disk spins off during disk operation and lubricant is reduced, resulting in a loss of protection. For this reason, a high-viscosity and low-volatile lubricant is suitably used, and the evaporation rate can be suppressed and the life of the disk drive can be extended.

In view of these lubrication mechanisms, requirements for low friction and low wear lubricants used in thin film magnetic recording media are as follows.
(1) Low volatility.
(2) Low surface tension for the surface replenishment function.
(3) There is an interaction between the terminal polar group and the disk surface.
(4) High thermal and oxidative stability so that there is no decomposition or decrease during the period of use.
(5) It is chemically inert to metals, glass, and polymers and does not generate wear powder on the head or guide.
(6) There must be no toxicity or flammability.
(7) Excellent boundary lubrication characteristics.
(8) Dissolve in an organic solvent.

  In recent years, ionic liquids have attracted attention as one of environmentally friendly solvents for synthesizing organic and inorganic materials in power storage materials, separation technologies, catalyst technologies, and the like. Ionic liquids fall into the large category of low melting point molten salts, but generally, those having a melting point of 100 ° C. or lower among them. Important characteristics of ionic liquids used as lubricants include low volatility, lack of flammability, thermal stability, and excellent dissolution performance. Therefore, ionic liquids are expected to be applied as new lubricants in extreme environments such as in vacuum and at high temperatures. In addition, a technique is known in which the controllability of a transistor is increased by a factor of 100 by using an ionic liquid for the gate of a single self-forming quantum dot transistor. In this technique, an ionic liquid forms an electric double layer and acts as an insulating film of about 1 nm, thereby obtaining a large electric capacity.

For example, friction and wear on the metal or ceramic surface may be reduced by using a certain ionic liquid as compared with a conventional hydrocarbon-based lubricant. For example, substituted with a fluoroalkyl group imidazole cation based ionic liquids are synthesized, tetrafluoroborate or hexafluorophosphate alkyl imidazolium, steel, aluminum, copper, single crystal SiO _2, silicon, sialon ceramics When used for (Si-Al-O-N), there is a report that it exhibits tribological properties superior to cyclic phosphazene (X-1P) and PFPE. In addition, there is a report that the friction of the ammonium-based ionic liquid is lower than that of the base oil in the boundary lubrication region from the elastic fluid. In addition, ionic liquids have been investigated for their effects as additives to base oils, and chemical and tribochemical reactions have been studied to understand the lubrication mechanism. There are few examples.

  Among the ionic liquids, a protic ionic liquid is a general term for compounds formed by an equivalent chemical reaction between a Bronsted acid and a Bronsted base. In a study on the interaction between carboxylic acid and amine by Kohler et al., It has been reported that a 1: 1 complex of carboxylic acid and amine can be formed with a chemical equivalent (see, for example, Non-Patent Documents 1 and 2). Perfluorooctanoic acid alkylammonium salt is a protonic ionic liquid (PIL), but it has been reported that it has a remarkable effect of reducing friction of magnetic recording media as compared to the above-described Z-DOL (patent). References 1 and 2, and Non-Patent Documents 3 to 5).

  However, these perfluorocarboxylic acid ammonium salts have a weak cation-anion interaction in the reaction shown in the following reaction formula (A), and the equilibrium is on the left at high temperatures due to Le Chatelier's law. , It becomes a dissociated neutral compound and the thermal stability is deteriorated. That is, proton transfer occurs at a high temperature, and the equilibrium moves to a neutral substance and dissociates (see, for example, Non-Patent Document 6).

Incidentally, the limit of the surface recording density of the hard disk is said to be 1-2.5 Tb / in ² . At present, the limit is approaching, but energetic development of high-capacity technology has been continued on the premise of miniaturization of magnetic particles. Technologies for increasing the capacity include reduction of effective flying height, introduction of single write (BMP), and the like.

  As a next-generation recording technology, there is “Heat Assisted Magnetic Recording”. FIG. 3 shows an outline of the heat-assisted magnetic recording. As a problem of this technique, since the recording portion is heated by a laser at the time of recording / reproducing, deterioration of durability due to evaporation or decomposition of the lubricant on the surface of the magnetic layer can be mentioned. Thermally assisted magnetic recording is likely to be exposed to high temperatures said to be 400 ° C. or higher for a short time, and is generally used as a lubricant for thin film magnetic recording media Z-DOL and carboxylic acid ammonium salt lubricants So there is concern about its thermal stability.

The ionic liquid is generally a substance having high thermal stability in order to form ions as described above. The equilibrium is shown in the following Scheme 1.

Here, HA represents a Bronsted acid and B represents a Bronsted base. The acid (HA) and the base (B) react to form a salt (A ⁻ HB ⁺ ) as shown in Scheme 1.
At this time, the dissociation constants K _a1 and K _b2 of the acid and the base can be expressed as the following Scheme 2 in a form including the concentration.

Since K _a1 and K _b2 vary greatly depending on the substance and in some cases have a large number of digits, which is inconvenient to handle, it is often expressed as a negative common logarithm. That is, as shown in the following Scheme 3, -log ₁₀ K _a1 = pK _a1 is defined, and an acid having a clearly smaller pK _a1 is more acidic.
Here, the difference ΔpKa in acid dissociation constant between acid and base will be discussed. The acid / base reaction is influenced by the acidity / basicity of each other (or the acidity of the conjugate acid), and the acidity difference ΔpKa can be expressed together in the following Scheme 3.

It can be seen that ΔpKa increases as the salt concentration [A ⁻ HB ⁺ ] increases with respect to the acid concentration and the base concentration.

Among them, Yoshizawa et al. Are prone to proton transfer when the difference in acid and base pKa (ΔpKa) is 10 or more.
[AH] + [B] ⇔ [A ⁻ HB ⁺ ]
It has been reported that the equilibrium of the above equation shifts to the ion side (right side) and the stability is further increased (for example, see Non-Patent Document 6). However, MacFarlane et al. Have reported that if ΔpKa is 4, proton transfer occurs and it is sufficient to obtain ionized PIL (see, for example, Non-Patent Document 7). In addition, from the energy level diagram, Dai et al. Explain that the thermal stability of the protic ionic liquid is greatly improved by the combination of a strong acid and a strong base (see, for example, Non-Patent Document 8). In addition, Watanabe et al. Strongly depend on ΔpKa for proton mobility and thermal stability of a protic ionic liquid, and DBU (1,8-diazabicyclo [5,4,0] unde-7-cene is used as a base. However, it is reported that the thermal stability of the ionic liquid is greatly improved by using an acid having a ΔpKa of 15 or more (for example, see Non-Patent Document 9). The degree of necessity is not fixed.

Japanese Patent No. 2581090 Japanese Patent No. 2629725

Kohler, F.A. Atrops, H .; , Kallall, H .; Liebermann, E .; Wilhelm, E .; , Ratkovics, F.M. , & Salamon, T .; , (1981a). Molecular Interactions in Mixtures of Carboxylic acids with amines. 1. Melting Curves and Viscosities, J.A. Phys. Chem. Vol. 85, no. 17, (Aug. 1981), pp. 2520-2524, ISSN: 0022-3654 Kohler, F.A. , Gopal, R .; Goetze, G .; Atrops, H .; , Demiriz, M .; A. Liebermann, E .; Wilhelm, E .; , Ratkovics, F.M. , & Paragyl, B.B. , (1981). Molecular Interactions in Mixtures of Carboxylic acids with amines. 2. Volumetric, Conductometric, and NMR Properties, J. MoI. Phys. Chem. Vol. 85, no. 17, pp. 2524-2529, ISSN: 0022-3654 Kondo, H .; , Seto, J .; , Haga. S. Ozawa, K .; (1989) Novell Lubricants for Magnetic Thin Film Media, Magnetic Soc. Japan, Vol. 13, Suppl. No. S1, pp. 213-218 Kondo, H .; , Seki, A .; Watanabe, H .; , & Seto, J. et al. , (1990). Frictional Properties of Novel Lubricants for Magnetic Thin Film Media, IEEE Trans. Magn. Vol. 26, no. 5, (Sep. 1990), pp. 2691-2693, ISSN: 0018-9464 Kondo, H .; , Seki, A .; , & Kita, A. (1994a). Comparison of an Amide and Amine Salt as Friction Modifiers for a Magnetic Thin Film Medium. Tribology Trans. Vol. 37, no. 1, (Jan. 1994), pp. 99-105, ISSN: 0569-8197 Yoshizawa, M .; Xu, W .; , Angel, C.I. A. , Ionic Liquids by Proton Transfer: Vapor pressure, Conductivity, and the Relevance of ΔpKa from Aqueous Solutions, J. Am. Am. Chem. Soc. , Vol. 125, pp. 15411-15419 (2003) Stomenovski, J. et al. , Izgorodina, E .; I. , MacFalane, D.M. R. , Ionicity and proton transfer in protic liquids, Phys. Chem. Chem. Phys. , 2010, Vol. 12, 10341 Luo, H .; Baker, G .; A. Lee, J .; S. , Pagni, R.A. M.M. Dai, S .; , Ultrastable Superbase-Derived Protic Ionic Liquids, J. et al. Phys. Chem. B Vol. 113, pp. 4181-4183 (2009) Luo, H .; Baker, G .; A. Lee, J .; S. , Pagni, R.A. M.M. Dai, S .; , Ultrastable Superbase-Derived Protic Ionic Liquids, J. et al. Phys. Chem. B Vol. 113, pp. 4181-4183 (2009) Miran, M.M. S. Kinoshita, H .; Yasuda, T .; Susan, M .; A. B. H. Watanabe, M .; , Physicochemical Properties Determined by ΔpKa for Protic Ionic Liquids Based on an Organic Super-strong Bases with Varied Bones Acids. Chem. Chem. Phys. , Vol 14, pp. 5178-5186 (2012)

  As described above, in the field of magnetic recording media, due to the lack of capability of the lubricant, there are still dissatisfaction with practical characteristics such as running performance, wear resistance and durability.

  The present invention has been proposed in view of such conventional circumstances, and provides an ionic liquid having excellent lubricity even at high temperatures, a lubricant having excellent lubricity even at high temperatures, and excellent practical characteristics. A magnetic recording medium is provided.

  As a result of intensive studies, the present inventor has found that the ionic liquid defines the carbon number of the hydrocarbon group of the Bronsted base and the difference between the pKa of the Bronsted acid and the pKa of the Bronsted base. The inventors have found that the object can be achieved, and have completed the present invention.

<1> containing an ionic liquid formed from Bronsted acid (HX) and Bronsted base (B),
The Bronsted base has a linear hydrocarbon group having 10 or more carbon atoms,
The lubricant characterized in that the difference between the pKa of the Bronsted acid in water and the pKa of the Bronsted base in water is 12 or more.
<2> The lubricant according to <1>, wherein the ionic liquid is represented by the following general formula (1).
In the general formula (1), at least one of R ₁ , R ₂ , R ₃ , and R ₄ is a hydrogen atom, and at least one of R ₁ , R ₂ , R ₃ , and R ₄ has a carbon number. It is a group containing 10 or more linear hydrocarbon groups.
<3> The lubricant according to <1>, wherein the Bronsted base is a cyclic amidine having a linear hydrocarbon group having 10 or more carbon atoms.
<4> The ionic liquid is the lubricant according to <3>, which is represented by the following general formula (2).
In the general formula (2), R ₁₁ represents a linear hydrocarbon group having 10 or more carbon atoms bonded to the carbon of the bicyclo ring.
<5> The lubricant according to any one of <1> to <4>, wherein the Bronsted acid is a sulfonic acid.
<6> The lubricant according to any one of <1> to <5>, wherein an exothermic peak temperature in differential thermal analysis (DTA) measurement of the ionic liquid is 370 ° C. or higher.
<7> The lubricant according to any one of <1> to <6>, wherein the hydrocarbon group is an alkyl group.
<8> containing an ionic liquid formed from Bronsted acid (HX) and Bronsted base (B),
The Bronsted base has a linear hydrocarbon group having 10 or more carbon atoms,
The lubricant characterized in that the difference between the pKa of the Bronsted acid in acetonitrile and the pKa of the Bronsted base in acetonitrile is 6 or more.
<9> The lubricant according to <8>, wherein the ionic liquid is represented by the following general formula (1).
In the general formula (1), at least one of R ₁ , R ₂ , R ₃ , and R ₄ is a hydrogen atom, and at least one of R ₁ , R ₂ , R ₃ , and R ₄ has a carbon number. It is a group containing 10 or more linear hydrocarbon groups.
<10> The Bronsted base is any one of a cyclic amidine having a linear hydrocarbon group having 10 or more carbon atoms and a cyclic guanidine having a linear hydrocarbon group having 10 or more carbon atoms. The lubricant according to <8>.
<11> The lubricant according to <10>, wherein the ionic liquid is represented by any one of the following general formula (2) and the following general formula (3).
In the general formula (2), R ₁₁ represents a linear hydrocarbon group having 10 or more carbon atoms bonded to the carbon of the bicyclo ring.
In the general formula (3), R ₂₁ represents a linear hydrocarbon group having 10 or more carbon atoms bonded to carbon or nitrogen of a bicyclo ring.
<12> The lubricant according to any one of <8> to <11>, wherein an exothermic peak temperature in differential thermal analysis (DTA) measurement of the ionic liquid is 370 ° C. or higher.
<13> The Bronsted acid is perfluoroalkylsulfonic acid, a compound represented by the following structural formula (A), a compound represented by the following structural formula (B), a compound represented by the following structural formula (C) And the lubricant according to any one of <8> to <12>, which is any of the compounds represented by the following structural formula (D).
<14> In a magnetic recording medium having at least a magnetic layer on a nonmagnetic support,
A magnetic recording medium comprising the lubricant according to any one of <1> to <13> in the magnetic layer.
<15> formed from Bronsted acid (HX) and Bronsted base (B),
The Bronsted base has a linear hydrocarbon group having 10 or more carbon atoms,
The ionic liquid is characterized in that the difference between the pKa of the Bronsted acid in water and the pKa of the Bronsted base in water is 12 or more.
<16> The ionic liquid according to <15>, which is represented by the following general formula (1).
In the general formula (1), at least one of R ₁ , R ₂ , R ₃ , and R ₄ is a hydrogen atom, and at least one of R ₁ , R ₂ , R ₃ , and R ₄ has a carbon number. It is a group containing 10 or more linear hydrocarbon groups.
<17> The ionic liquid according to <15>, wherein the Bronsted base is a cyclic amidine having a linear hydrocarbon group having 10 or more carbon atoms.
<18> The ionic liquid according to <17>, which is represented by the following general formula (2).
In the general formula (2), R ₁₁ represents a linear hydrocarbon group having 10 or more carbon atoms bonded to the carbon of the bicyclo ring.
<19> The ionic liquid according to any one of <15> to <18>, wherein the Bronsted acid is a sulfonic acid.
<20> The ionic liquid according to any one of <15> to <19>, wherein an exothermic peak temperature in differential thermal analysis (DTA) measurement is 370 ° C. or higher.
<21> The ionic liquid according to any one of <15> to <20>, wherein the hydrocarbon group is an alkyl group.
<22> the Bronsted base is, octadecylamine _{(C 18 H 37 NH 2)} , decylamine _{(C 10 H 21 NH 2)} , tetradecyl amine _{(C 14 H 29 NH 2)} , eicosyl amine _(C 20 _{H 41} NH ₂ ), oleylamine (C ₁₈ H ₃₅ NH ₂ ), 2-heptylundecylamine (CH ₃ (CH ₂ ) _n CH (C ₇ H ₁₅ ) NH ₂ ), and the following structural formula (1) The ionic liquid according to any one of <15> to <21>, which is any one of compounds.
<23> formed from Bronsted acid (HX) and Bronsted base (B),
The Bronsted base has a linear hydrocarbon group having 10 or more carbon atoms,
The ionic liquid is characterized in that the difference between the pKa of the Bronsted acid in acetonitrile and the pKa of the Bronsted base in acetonitrile is 6 or more.
<24> The ionic liquid according to <23>, which is represented by the following general formula (1).
In the general formula (1), at least one of R ₁ , R ₂ , R ₃ , and R ₄ is a hydrogen atom, and at least one of R ₁ , R ₂ , R ₃ , and R ₄ has a carbon number. It is a group containing 10 or more linear hydrocarbon groups.
<25> The Bronsted base is any one of a cyclic amidine having a linear hydrocarbon group having 10 or more carbon atoms and a cyclic guanidine having a linear hydrocarbon group having 10 or more carbon atoms. The ionic liquid according to <23>.
<26> The ionic liquid according to <25>, which is represented by any one of the following general formula (2) and the following general formula (3).
In the general formula (2), R ₁₁ represents a linear hydrocarbon group having 10 or more carbon atoms bonded to the carbon of the bicyclo ring.
In the general formula (3), R ₂₁ represents a linear hydrocarbon group having 10 or more carbon atoms bonded to carbon or nitrogen of a bicyclo ring.
<27> The ionic liquid according to any one of <23> to <26>, wherein an exothermic peak temperature in differential thermal analysis (DTA) measurement is 370 ° C. or higher.
<28> The Bronsted acid is perfluoroalkylsulfonic acid, a compound represented by the following structural formula (A), a compound represented by the following structural formula (B), a compound represented by the following structural formula (C) And the ionic liquid according to any one of <23> to <27>, which is any of the compounds represented by the following structural formula (D).
<29> the Bronsted base is, octadecylamine _{(C 18 H 37 NH 2)} , decylamine _{(C 10 H 21 NH 2)} , tetradecyl amine _{(C 14 H 29 NH 2)} , eicosyl amine _(C 20 _{H 41} NH ₂ ), oleylamine (C ₁₈ H ₃₅ NH ₂ ), 2-heptylundecylamine (CH ₃ (CH ₂ ) _n CH (C ₇ H ₁₅ ) NH ₂ ), a compound represented by the following structural formula (2) And the ionic liquid according to any one of <23> to <28>, which is any one of compounds represented by the following structural formula (3).

  According to the present invention, thermal stability such as evaporation and thermal decomposition of a lubricant can be improved, and excellent lubrication characteristics can be maintained over a long period of time. Further, when a lubricant is used for a magnetic recording medium, it is excellent in lubrication characteristics and can improve practical characteristics such as runnability, wear resistance and durability.

FIG. 1 is a sectional view showing an example of a hard disk according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing an example of a magnetic tape according to an embodiment of the present invention. FIG. 3 is a schematic diagram showing heat-assisted magnetic recording. FIG. 4 is a diagram illustrating a TG measurement result in the example. FIG. 5 is an FTIR spectrum of the product of Example 36. FIG. 6 is a TG / DTA measurement result of the product of Example 36. FIG. 7 is an FTIR spectrum of the product of Example 37. FIG. 8 is a TG / DTA measurement result of the product of Example 37. FIG. 9 is an FTIR spectrum of the product of Example 38. FIG. 10 shows the TG / DTA measurement result of the product of Example 38. FIG. 11 is an FTIR spectrum of the product of Example 39. FIG. 12 shows the TG / DTA measurement result of the product of Example 39. FIG. 13 is an FTIR spectrum of the product of Example 40. FIG. 14 shows the TG / DTA measurement result of the product of Example 40. FIG. 15 is an FTIR spectrum of the product of Example 41. FIG. 16 is a TG / DTA measurement result of the product of Example 41. FIG. 17 is an FTIR spectrum of the product of Example 42. FIG. 18 shows the TG / DTA measurement result of the product of Example 42. FIG. 19 is an FTIR spectrum of the product of Comparative Example 27. 20 is a TG / DTA measurement result of the product of Comparative Example 27. FIG. FIG. 21 is an FTIR spectrum of the product of Comparative Example 28. FIG. 22 is a TG / DTA measurement result of the product of Comparative Example 28.

Hereinafter, embodiments of the present invention will be described in detail in the following order with reference to the drawings.
1. 1. Lubricant and ionic liquid 2. Magnetic recording medium Example

<1. Lubricant and ionic liquid>
The lubricant shown as one embodiment of the present invention contains an ionic liquid represented by the general formula X ^- B ^+, and a Bronsted base (B) is preferably a linear hydrocarbon group having preferably 10 or more carbon atoms. A compound having an acid (for example, an ammonium salt) is used.

The ionic liquid in the present embodiment is a protonic ionic liquid synthesized by neutralization of Bronsted acid (HX) and Bronsted base (B).
This ionic liquid has excellent thermal stability because the difference between pKa of Bronsted acid in water and pKa of Bronsted base in water (ΔpKa: pKa of Bronsted base-pKa of Bronsted acid) is 12 or more. Can demonstrate its sexuality.
Further, this ionic liquid has a difference between the pKa of Bronsted acid in acetonitrile and the pKa of Bronsted base in acetonitrile (ΔpKa: pKa of Bronsted base−pKa of Bronsted acid) is 6 or more, Excellent thermal stability can be exhibited. For pKa in acetonitrile, see, for example, Blackwell Scientific Publications, Oxford, 1990, and J. Org. Org. Chem. 2011, Vol. 76, pp. 391-395 and the like.

Watanabe et al. Show that the proton mobility and thermal stability of a protic ionic liquid depend greatly on ΔpKa, and DBU (1,8-diazabicyclo [5,4,0] unde-7-cene is used as a base. Have reported that the thermal stability of the ionic liquid is greatly improved by using an acid having a ΔpKa of 15 or more (Miran, MS, Kinoshita, H., Yasuda, T., Susan). , M. A. B. H., Watanabe, M., Physicochemical Properties Determined by [Delta] pKa for Protic Ionic Liquids, Based on an Organic Super-strong Bronze. hem. Chem. Phys., Vol 14, pp.5178-5186 (2012)).
However, the consideration of how much ΔpKa is required depending on the application has not been fixed.
As a result of intensive studies, the present inventors have found that the thermal stability mechanism differs depending on the numerical value of ΔpKa, and when the ΔpKa is small by analysis using TG / DTA, the weight loss of the ionic liquid is endothermic. In the case where ΔpKa is large while it is evaporation, it was confirmed that the weight loss of the ionic liquid is exothermic and thermal decomposition is dominant.
In the ionic liquid, since the difference between the pKa of Bronsted acid in water and the pKa of Bronsted base in water (ΔpKa: pKa of Bronsted base-pKa of Bronsted acid) is 12 or more, excellent heat It has been found that it exhibits stability and is useful as a lubricant.
Further, in the ionic liquid, the difference between the pKa of the Bronsted acid in acetonitrile and the pKa of the Bronsted base in acetonitrile (ΔpKa: pKa of the Bronsted base−pKa of the Bronsted acid) is 6 or more. It has been found that it exhibits excellent thermal stability and is useful as a lubricant.

Here, pKa in the present specification is an acid dissociation constant, which is an acid dissociation constant in water or an acid dissociation constant in acetonitrile.
The acid dissociation constant in water is, for example, J. Chem. Res. , Synop. It can be measured with reference to the method described in 1994, 212-213. Specifically, it can be measured by a combination of a spectrometer and a potentiometric measurement.
Said acid dissociation constant in acetonitrile is Org. Chem. 1998, 63, p. 7868, or J.H. Org. Chem. 1997, 62, p. However, the acid is dissolved in acetonitrile, titrated with a base, and calculated from a spectrum measured using a UV-vis spectrometer.

The ionic liquid is excellent in solubility in a highly volatile solvent such as lower alcohol (alcohol having 1 to 3 carbon atoms) or ether. Therefore, a solution can be easily prepared at the time of use. Further, when the solution is applied and used, the solvent can be easily removed.
In addition, since the compound in the present invention has a long-chain alkyl group, it has a relatively high melting point, can be produced by recrystallization, and is very easy to produce.

There is no restriction | limiting in particular as exothermic peak temperature in the differential thermal analysis (DTA) measurement of the said ionic liquid, Although it can select suitably according to the objective, 370 degreeC or more is a point which exhibits the outstanding thermal stability. Preferably, 400 degreeC-500 degreeC is more preferable.
The differential thermal analysis can be performed, for example, by the following method.
Using EXSTAR6000 manufactured by Seiko Instruments Inc., measurement is performed in a temperature range of 30 ° C. to 600 ° C. at a temperature increase rate of 10 ° C./min while introducing air at a flow rate of 200 mL / min. A gas chromatographic mass spectrometer is an Agilent 6890/5975 MSD. The column was DB-1 (15 m, diameter 0.25 mm, film thickness 0.1 μm), the injection temperature was 280 ° C., the initial column temperature was held at 40 ° C. for 5 minutes, and then the heating rate was 20 ° C./min to 340 ° C. Raise the temperature and hold at that temperature. The mass unit is 5975 MSD, MS detection method is EI ⁺ , quadrupole temperature is 150 ° C., ion source temperature is 300 ° C., mass scan range is m / z 33-700, and calibration uses PFTBA.

The upper limit value of ΔpKa in water is not particularly limited and may be appropriately selected depending on the intended purpose. However, the ΔpKa in water is preferably 25 or less, and more preferably 21 or less.
The upper limit value of ΔpKa in acetonitrile is not particularly limited and may be appropriately selected depending on the intended purpose. The ΔpKa in acetonitrile is preferably 40 or less, and more preferably 35 or less.

As the Bronsted acid, one that satisfies the condition that the difference (ΔpKa) between pKa of Bronsted acid (HX) in water and pKa of Bronsted base (B) in water is 12 or more is used.
The Bronsted acid is one that satisfies the condition that the difference (ΔpKa) between the pKa of Bronsted acid (HX) in acetonitrile and the pKa of Bronsted base (B) in acetonitrile is 6 or more. Used.
Examples of such Bronsted acids include those described in the literature J. Org. Chem. 2005, Vol. 70, p. 1019, and preferably has a small pKa of Bronsted acid (HX), bis ((trifluoromethyl) sulfonyl) imide ((CF ₃ SO ₂ ) ₂ NH), bis ( Nonafluorobutylsulfonyl) imide, sulfonylimides such as cyclo-hexafluoropropane-1,3-bis (sulfonyl), trifluoromethanesulfonic acid (CF ₃ SO ₃ H), sulfuric acid (H ₂ SO ₄ ), methanesulfonic acid ( Sulfonic acids such as CH ₃ SO ₃ H) and perfluorooctane sulfonic acid (C ₈ F ₁₇ SO ₃ H) are used.

Other examples of the Bronsted acid include perfluoroalkylsulfonic acid, a compound represented by the following structural formula (A), a compound represented by the following structural formula (B), and the following structural formula (C). It may be a compound or a compound represented by the following structural formula (D).

  In addition, non-patent literature (Agnes Kutt, Tomas Rodima, Jaan Samea, Elin Raamat, Vahur Maemets, Ivari Kaljand, Ilmar A. Kompel, Ilmar A. Kompel, Ilmar A. Kompel, Ilmar A. Yum. M. Yagupolskii, Edward Bernhardt, Helg Willner, and Ivo Leito, “Equilibrium Acids of Superacids”, J. Org. Also for Can be.

There is no restriction | limiting in particular as pKa of the said Bronsted acid in water, Although it can select suitably according to the objective, -18--3 are preferable.
There is no restriction | limiting in particular as pKa of the said Bronsted acid in acetonitrile, Although it can select suitably according to the objective, -5-12 are preferable.

The Bronsted base satisfies the condition that the difference (ΔpKa) between the pKa of the Bronsted acid (HX) in water and the pKa of the Bronsted base (B) in water is 12 or more, preferably carbon An organic base compound (for example, ammonium salt) having a linear hydrocarbon group having a number of 10 or more is used. By coal hydrocarbon chain is a long chain, the friction coefficient is reduced, thereby improving the lubricating properties.
The Bronsted base satisfies the condition that the difference (ΔpKa) between the pKa of the Bronsted acid (HX) in acetonitrile and the pKa of the Bronsted base (B) in acetonitrile is 6 or more, preferably An organic base compound (for example, ammonium salt) having a linear hydrocarbon group having 10 or more carbon atoms is used. By coal hydrocarbon chain is a long chain, the friction coefficient is reduced, thereby improving the lubricating properties.
As the organic base compound, a compound having a large pKa is preferable.
Examples of the organic base compound include amines, hydroxylamines, imines, oximes, hydrazines, hydrazones, guanidines, amidines, sulfoamides, imides, amides, thioamides, carbamates, nitriles, Examples include ureas, urethanes and cyclic heterocycles. Examples of the cyclic heterocycle include pyrrole, indole, azole, oxazole, triazole, tetraazole, and imidazole.

  Other examples of the Bronsted base include non-patent literature (Ivari Kaljurand, Agnes Ku.tt., Lilli Soova.li, Tomas Rodima, Vahur Ma. Self-Consistent Spectrophotometric Basic Scale in Acetonitile to a Full Span of 28 pKa Units: Unified of Difficult Basis. Or the like can also be used organic bases are.

  The upper limit of the carbon number of the linear hydrocarbon group having 10 or more carbon atoms is not particularly limited and may be appropriately selected depending on the purpose. From the viewpoint of procurement of raw materials, the carbon number is 25 or less is preferable, and 20 or less is more preferable.

  The hydrocarbon group may be linear, and may be either a saturated hydrocarbon group, an unsaturated hydrocarbon group partially having a double bond, or an unsaturated branched hydrocarbon group partially having a branch. . Among these, an alkyl group which is a saturated hydrocarbon group is preferable from the viewpoint of wear resistance. Moreover, it is also preferable that it is a linear hydrocarbon group which does not have a branch in part.

There is no restriction | limiting in particular as pKa of the said Bronsted base in water, Although it can select suitably according to the objective, 9-30 are preferable.
There is no restriction | limiting in particular as pKa of the said Bronsted base in acetonitrile, Although it can select suitably according to the objective, 15-35 are preferable.

  Examples of the Bronsted base include a compound containing nitrogen having a positive charge when an ion pair is formed with the Bronsted acid. Examples of such compounds include amines, hydroxylamines, imines, oximes, hydrazines, hydrazones, guanidines, amidines, sulfoamides, imides, amides, thioamides, carbamates, nitriles, Examples include ureas, urethanes and cyclic heterocycles. Examples of the cyclic heterocycle include pyrrole, indole, azole, oxazole, triazole, tetraazole, and imidazole. Moreover, the said aliphatic amine, aromatic amine, cyclic amine, amidine, etc. are mentioned. Examples of the aliphatic amine include a primary aliphatic amine, a secondary aliphatic amine, and a tertiary aliphatic amine. Examples of the aromatic amine include aniline, diphenylamine, and 4-aminopyridine. Examples of the cyclic amine include pyrrolidine, 2,2,6,6-tetramethylpiperidine, quinuclidine and the like. Examples of the amidine include cyclic amidine.

Specific Bronsted base, octadecylamine _{(C 18 H 37 NH 2)} , decylamine _{(C 10 H 21 NH 2)} , tetradecyl amine _{(C 14 H 29 NH 2)} , eicosyl amine _(C 20 _{H 41} An aliphatic amine such as NH ₂ ), oleylamine (C ₁₈ H ₃₅ NH ₂ ), 2-heptylundecylamine (CH ₃ (CH ₂ ) _n CH (C ₇ H ₁₅ ) NH ₂ ) is preferably used. However, it goes without saying that the structure of the amine is not limited to this. For example, a hydrocarbon chain may be introduced into a heterocyclic compound, alicyclic compound, or aromatic compound. In addition, a compound represented by the following structural formula (1), a compound represented by the following structural formula (2), and a compound represented by the following structural formula (3) are also preferably used.

  An ionic liquid using an aliphatic amine as the Bronsted base is represented by the following general formula (1).

In the general formula (1), at least one of R ₁ , R ₂ , R ₃ , and R ₄ is a hydrogen atom, and at least one of R ₁ , R ₂ , R ₃ , and R ₄ has a carbon number. It is a group containing 10 or more linear hydrocarbon groups. R other than the straight-chain hydrocarbon having 10 or more carbon atoms is preferably any of a branched hydrocarbon, an aromatic ring, an alicyclic ring, a hydrocarbon having an unsaturated bond, or hydrogen. Moreover, it may be a heterocyclic compound and may be substituted with halogen.
The group containing a linear hydrocarbon group having 10 or more carbon atoms is preferably a linear hydrocarbon group having 10 or more carbon atoms.

  In the ionic liquid, the Bronsted base is a cyclic amidine having a linear hydrocarbon group having 10 or more carbon atoms, or a cyclic guanidine having a linear hydrocarbon group having 10 or more carbon atoms. It is preferable. Examples of the cyclic amidine include imidazole, benzimidazole, 1,8-diazabicyclo (5,4,0) -undecene-7 (DBU), 1,5-diazabicyclo (4,3,0) -nonene-5 ( DBN). The pKa of imidazole is 14, the pKa of DBU in water is 12.5, and the pKa of DBN in water is 12.7. Examples of the cyclic guanidine include 1,5,7-triazabicyclo [4.4.0] -5-decene (TBD). The Bronsted base is described in, for example, the literature Chem. Eur. J. et al. 2012, Vol. 18, p. 3621, or J.P. Org. Chem. 2005, Vol. 70, p. A compound called super base shown in 1019 can be used.

The ionic liquid is preferably a compound represented by the following general formula (2), and more preferably a compound represented by the following general formula (2-1).
The ionic liquid is preferably a compound represented by the following general formula (3), and more preferably a compound represented by the following general formula (3-1).
In the general formula (2), R ₁₁ represents a linear hydrocarbon group having 10 or more carbon atoms bonded to the carbon of the bicyclo ring.
In the general formula (2-1), R ₁₁ represents a linear hydrocarbon group having 10 or more carbon atoms.
In the general formula (3), R ₂₁ represents a linear hydrocarbon group having 10 or more carbon atoms bonded to carbon or nitrogen of a bicyclo ring.
In the general formula (3-1), R ₂₁ represents a linear hydrocarbon group having 10 or more carbon atoms.

  Here, an example of the ionic liquid synthesis method will be described. The ionic liquid is synthesized from a Bronsted acid and a Bronsted base. Specifically, it can be obtained, for example, by neutralizing sulfonic acid and an organic base compound by mixing them in an equivalent amount.

Alternatively, the aliphatic amine can be neutralized with nitric acid to obtain an ammonium nitrate salt, followed by anion exchange. For example, by performing anion exchange with an equivalent amount of bis (trifluoromethanesulfonyl) amidolithium salt (Li [(CF ₃ SO ₂ ) ₂ N]) with respect to an ammonium nitrate salt as shown in the following reaction formula (2), An ionic liquid can be obtained.

  As the lubricant in the present embodiment, the ionic liquid described above may be used alone, or may be used in combination with a conventionally known lubricant. For example, it can be used in combination with long chain carboxylic acid, long chain carboxylic acid ester, perfluoroalkyl carboxylic acid ester, carboxylic acid perfluoroalkyl ester, perfluoroalkyl carboxylic acid perfluoroalkyl ester, perfluoropolyether derivative, etc. Is possible.

  In order to maintain the lubricating effect under severe conditions, an extreme pressure agent may be used in combination at a mass ratio of about 30:70 to 70:30. The extreme pressure agent acts to prevent friction and wear by forming a reaction product film by reacting with the metal surface due to frictional heat generated when metal contact occurs partially in the boundary lubrication region. Is. As the extreme pressure agent, for example, any of a phosphorus extreme pressure agent, a sulfur extreme pressure agent, a halogen extreme pressure agent, an organometallic extreme pressure agent, a composite extreme pressure agent, and the like can be used.

  Moreover, you may use a rust preventive agent together as needed. The rust inhibitor may be any rust inhibitor that can be used as a rust inhibitor for this type of magnetic recording medium. For example, phenols, naphthols, quinones, heterocyclic compounds containing nitrogen atoms, oxygen atoms And heterocyclic compounds containing sulfur atoms, and the like. The rust preventive agent may be used as a lubricant, but a magnetic layer is formed on a nonmagnetic support, a rust preventive layer is applied thereon, and then a lubricant layer is applied. Thus, it may be applied in two or more layers.

  In addition, as the solvent for the lubricant, for example, alcohol solvents such as isopropyl alcohol (IPA) and ethanol can be used alone or in combination. For example, it can be used by mixing a hydrocarbon solvent such as normal hexane or a fluorine solvent.

<2. Magnetic recording media>
Next, a magnetic recording medium using the above-described lubricant will be described. A magnetic recording medium shown as an embodiment of the present invention has at least a magnetic layer on a nonmagnetic support, and the magnetic layer contains the above-mentioned lubricant.

  The lubricant in the present embodiment can be applied to a so-called metal thin film type magnetic recording medium in which a magnetic layer is formed on the surface of a nonmagnetic support by a technique such as vapor deposition or sputtering. The present invention can also be applied to a magnetic recording medium having a configuration in which an underlayer is interposed between a nonmagnetic support and a magnetic layer. Examples of such a magnetic recording medium include a magnetic disk and a magnetic tape.

  FIG. 1 is a cross-sectional view showing an example of a hard disk. This hard disk has a structure in which a substrate 11, an underlayer 12, a magnetic layer 13, a carbon protective layer 14, and a lubricant layer 15 are sequentially laminated.

  FIG. 2 is a cross-sectional view showing an example of a magnetic tape. This magnetic tape has a structure in which a backcoat layer 25, a substrate 21, a magnetic layer 22, a carbon protective layer 23, and a lubricant layer 24 are sequentially laminated.

  In the magnetic disk shown in FIG. 1, the nonmagnetic support corresponds to the substrate 11 and the underlayer 12, and in the magnetic tape shown in FIG. 2, the nonmagnetic support corresponds to the substrate 21. When a rigid substrate such as an Al alloy plate or glass plate is used as the non-magnetic support, an oxide film such as anodized or Ni-P film may be formed on the substrate surface to harden the surface. Good.

  The magnetic layers 13 and 22 are formed as a continuous film by a technique such as plating, sputtering, vacuum deposition, or plasma CVD. As the magnetic layers 13 and 22, metals such as Fe, Co, Ni, Co—Ni alloys, Co—Pt alloys, Co—Ni—Pt alloys, Fe—Co alloys, Fe—Ni alloys, In-plane magnetization recording metal magnetic film made of Fe-Co-Ni alloy, Fe-Ni-B alloy, Fe-Co-B alloy, Fe-Co-Ni-B alloy, etc., Co-Cr alloy Examples thereof include perpendicular magnetic recording metal magnetic thin films such as thin films and Co—O thin films.

  In particular, when an in-plane magnetization recording metal magnetic thin film is formed, a nonmagnetic material such as Bi, Sb, Pb, Sn, Ga, In, Ge, Si, or Tl is previously formed on the nonmagnetic support as the underlayer 12. In addition, metal magnetic materials are vapor-deposited or sputtered from the vertical direction, and these non-magnetic materials are diffused in the magnetic metal thin film to eliminate orientation and ensure in-plane isotropy and improve coercive force. You may do it.

Further, hard protective layers 14 and 23 such as a carbon film, a diamond-like carbon film, a chromium oxide film, and a SiO ₂ film may be formed on the surfaces of the magnetic layers 13 and 22.

As a method for retaining such a lubricant in such a metal thin film type magnetic recording medium, as shown in FIGS. 1 and 2, the top of the surface of the magnetic layers 13 and 22 or the surface of the protective layers 14 and 23 is used. The method of coating is mentioned. The coating amount of the lubricant is ^{preferably 0.1mg / m 2 ~100mg / m 2} , more preferably ^{0.5mg / m 2 ~30mg / m 2} , 0.5mg / m 2 ~ Particularly preferred is 20 mg / m ² .

  As shown in FIG. 2, in the metal thin film type magnetic tape, a back coat layer 25 may be formed as necessary in addition to the metal magnetic thin film as the magnetic layer 22.

  The back coat layer 25 is formed by adding a carbon fine powder for imparting conductivity to the resin binder and an inorganic pigment for controlling the surface roughness. In the present embodiment, the aforementioned lubricant may be added to the back coat layer 25 by internal addition or top coat. Further, the above-described lubricant may be added to both the magnetic layer 22 and the back coat layer 25 by internal addition or top coat.

  As another embodiment, the lubricant can be applied to a so-called coating type magnetic recording medium in which a magnetic coating film is formed as a magnetic layer by applying a magnetic paint to the surface of a nonmagnetic support. is there. In the coating-type magnetic recording medium, any conventionally known magnetic powder, resin binder and the like constituting the nonmagnetic support, the magnetic coating film, and the like can be used.

  For example, as the nonmagnetic support, for example, a polymer support formed of a polymer material typified by polyesters, polyolefins, cellulose derivatives, vinyl resins, polyimides, polyamides, polycarbonates and the like. Examples thereof include a metal substrate made of aluminum alloy, titanium alloy, etc., a ceramic substrate made of alumina glass, etc., a glass substrate, and the like. Moreover, the shape is not limited at all, and any shape such as a tape shape, a sheet shape, or a drum shape may be used. Further, the non-magnetic support may be subjected to a surface treatment so as to form fine irregularities in order to control the surface property.

Examples of the magnetic powder include ferromagnetic iron oxide particles such as γ-Fe ₂ O ₃ and cobalt-coated γ-Fe ₂ O ₃ , ferromagnetic chromium dioxide particles, metals such as Fe, Co, Ni, and the like. Examples thereof include ferromagnetic metal particles made of an alloy containing hexagonal plate-like ferrite fine particles.

  Examples of the resin binder include vinyl chloride, vinyl acetate, vinyl alcohol, vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, butadiene, acrylonitrile, or a combination of these two or more, polyurethane Resins, polyester resins, epoxy resins and the like are exemplified. In these binders, a hydrophilic polar group such as a carboxylic acid group, a carboxyl group or a phosphoric acid group may be introduced in order to improve the dispersibility of the magnetic powder.

  In addition to the magnetic powder and the resin binder, a dispersant, an abrasive, an antistatic agent, an antirust agent, and the like may be added to the magnetic coating film as an additive.

  Examples of a method for retaining the lubricant in such a coating type magnetic recording medium include a method of internally adding the magnetic layer constituting the magnetic coating film formed on the nonmagnetic support, There is a method of top-coating the surface of the layer, or a combination of both. Moreover, when adding the said lubricant internally in the said magnetic coating film, it adds in 0.2 mass part-20 mass parts with respect to 100 mass parts of said resin binders.

Further, in the case of top coat the lubricant on the surface of the magnetic layer preferably has an applied amount is ^{0.1mg / m 2 ~100mg / m 2} , 0.5mg / m 2 ~20mg / m ² is more preferable. In addition, as a deposition method when the lubricant is top-coated, an ionic liquid is dissolved in a solvent, and the obtained solution is applied or sprayed, or a magnetic recording medium is immersed in this solution.

In the present embodiment, an ionic liquid formed from a Bronsted acid and preferably a Bronsted base having a linear hydrocarbon group having 10 or more carbon atoms, and having a pKa difference (ΔpKa) in water of 12 or more. By using a lubricant containing, a good lubricating action can be exhibited, the friction coefficient can be reduced, and high thermal stability can be obtained. Further, this lubricating action is not impaired even under severe conditions such as high temperature, low temperature, high humidity, and low humidity.
Further, in the present embodiment, it is formed from a Bronsted acid and preferably a Bronsted base having a linear hydrocarbon group having 10 or more carbon atoms, and the difference in pKa (ΔpKa) in acetonitrile is 6 or more. By using a lubricant containing a certain ionic liquid, it is possible to exhibit a good lubricating action, reduce the friction coefficient, and obtain high thermal stability. Further, this lubricating action is not impaired even under severe conditions such as high temperature, low temperature, high humidity, and low humidity.

  Therefore, the magnetic recording medium to which the lubricant according to the present embodiment is applied can exhibit excellent running performance, wear resistance, durability, and the like due to the lubricating action, and can further improve the thermal stability.

<3. Example>
Hereinafter, specific examples of the present invention will be described. In this example, an ionic liquid was synthesized to produce a lubricant containing the ionic liquid. Then, magnetic disks and magnetic tapes were prepared using a lubricant, and disk durability and tape durability were evaluated, respectively. The production of the magnetic disk, the disk durability test, the production of the magnetic tape, and the tape durability test were performed as follows. The present invention is not limited to these examples.

<Manufacture of magnetic disks>
For example, in accordance with International Publication No. 2005/068589, a magnetic thin film was formed on a glass substrate to produce a magnetic disk as shown in FIG. Specifically, a chemically strengthened glass disk made of aluminum silicate glass with an outer diameter of 65 mm, an inner diameter of 20 mm, and a disk thickness of 0.635 mm is prepared, and the surface is polished so that Rmax is 4.8 nm and Ra is 0.43 nm. did. The glass substrate was subjected to ultrasonic cleaning in pure water and isopropyl alcohol (IPA) having a purity of 99.9% or more for 5 minutes each, left in IPA saturated vapor for 1.5 minutes and then dried. did.

  On this substrate 11, a NiAl alloy (Ni: 50 mol%, Al: 50 mol%) thin film is formed as a seed layer by DC magnetron sputtering, and a CrMo alloy (Cr: 80 mol%, Mo: 20 mol) is used as the underlayer 12. %) A thin film having a thickness of 8 nm and a CoCrPtB alloy (Co: 62 mol%, Cr: 20 mol%, Pt: 12 mol%, B: 6 mol%) as a magnetic layer 13 were sequentially formed to a thickness of 15 nm.

  Next, a carbon protective layer 14 made of amorphous diamond-like carbon is formed to 5 nm by plasma CVD, and the disk sample is ultrasonicated in isopropyl alcohol (IPA) having a purity of 99.9% or more for 10 minutes in a cleaner. Cleaning was performed to remove impurities on the disk surface, and then drying was performed. Thereafter, the lubricant layer 15 was formed to a thickness of about 1 nm by applying the ionic liquid IPA solution to the disk surface by a dip coating method in an environment of 25 ° C. and 50% relative humidity (RH).

<Disk durability test>
Using a commercially available strain gauge type disk friction and wear tester, after mounting the hard disk on the rotating spindle with a tightening torque of 14.7 Ncm, the center of the air bearing surface on the inner circumference side of the hard disk of the head slider is A head slider was mounted on the hard disk so as to be 17.5 mm from the center, and a CSS durability test was conducted. The head used for this measurement is an IBM 3370 type inline type head, the material of the slider is Al ₂ O ₃ —TiC, and the head load is 63.7 mN. In this test, the maximum value of the frictional force was monitored for each CSS (Contact, Start, Stop) in an environment of clean cleanliness 100 and 25 ° C. 60% RH. The number of times the friction coefficient exceeded 1.0 was taken as the result of the CSS durability test. In the result of the CSS endurance test, when it exceeded 50,000 times, “> 50,000” was displayed. Moreover, in order to investigate heat resistance, the CSS durability test after performing the heat test for 3 minutes at the temperature of 300 degreeC was similarly done.

<Manufacture of magnetic tape>
A magnetic tape having a cross-sectional structure as shown in FIG. 2 was produced. First, Co was deposited on a substrate 21 made of a Toray Mikutron (aromatic polyamide) film having a thickness of 5 μm by an oblique deposition method to form a magnetic layer 22 made of a ferromagnetic metal thin film having a thickness of 100 nm. Next, a carbon protective layer 23 made of carbon-like carbon having a thickness of 10 nm was formed on the surface of the ferromagnetic metal thin film by plasma CVD, and then cut into a width of 6 mm. An ionic liquid dissolved in IPA was applied on the magnetic layer 22 so as to have a film thickness of about 1 nm to form a lubricant layer 24, thereby preparing a sample tape.

<Tape durability test>
About each sample tape, the still durability under a temperature of -5 ° C environment and a temperature of 40 ° C and 30% RH, and the friction coefficient and shuttle durability under a temperature of -5 ° C and a temperature of 40 ° C and 90% RH. Measurements were made. Still durability evaluated the decay time until the output in a pause state fell -3dB. Shuttle durability was evaluated by the number of shuttles until the output decreased by 3 dB after repeatedly running the shuttle for 2 minutes each time. Moreover, in order to investigate heat resistance, the durability test after performing the heat test for 10 minutes at the temperature of 100 degreeC was similarly done.

<3.1 Effect of difference (ΔpKa) between pKa of Bronsted acid and pKa of Bronsted base>
Ionic liquids were synthesized in which the difference (ΔpKa) between pKa of Bronsted acid and pKa of Bronsted base was different. Then, a lubricant containing an ionic liquid was used for the magnetic recording medium, and the influence of the difference (ΔpKa) between the pKa of the Bronsted acid and the pKa of the Bronsted base was examined.

  In addition, pKa in Examples 1-35 and Comparative Examples 1-26 is pKa in water. The pKa in Examples 36 to 56 and Comparative Examples 27 to 32 is pKa in acetonitrile.

Example 1
[Ionic liquid 1]
As shown in Table 2, bis (trifluoromethylsulfonyl) imide (pKa = −10) was used as the Bronsted acid, and octadecylamine (pKa = having a straight-chain hydrocarbon group having 18 carbon atoms as the Bronsted base). 10.7) was used. The difference (ΔpKa) between pKa of Bronsted acid and pKa of Bronsted base was 20.7. After neutralizing octadecylamine with nitric acid to obtain an ammonium nitrate salt, anion exchange with bis (trifluoromethylsulfonyl) imide lithium salt (Li [(CF ₃ SO ₂ ) ₂ N]) equivalent to the ammonium nitrate salt The ionic liquid 1 was synthesized. The ionic liquid 1 is the same compound as the ionic liquid 12 described later, and the details of the synthesis method are as described in the method for synthesizing the ionic liquid 12.

(Example 2)
[Ionic liquid 2]
As shown in Table 2, trifluoromethanesulfonic acid (CF ₃ SO ₃ H, pKa = −7) was used as the Bronsted acid, and octadecylamine having a linear hydrocarbon group having 18 carbon atoms as the Bronsted base ( pKa = 10.7) was used. The difference (ΔpKa) between pKa of Bronsted acid and pKa of Bronsted base was 17.7. Ionic liquid 2 was synthesized by mixing and neutralizing an equivalent amount of trifluorometasulfonic acid with respect to octadecylamine.

(Example 3)
[Ionic liquid 3]
As shown in Table 2, sulfuric acid (H ₂ SO ₄ , pKa = −3) was used as the Bronsted acid, and octadecylamine having a linear hydrocarbon group having 18 carbon atoms as the Bronsted base (pKa = 10. 7) was used. The difference (ΔpKa) between pKa of Bronsted acid and pKa of Bronsted base was 13.7. Ionic liquid 3 was synthesized by mixing and neutralizing an equivalent amount of sulfuric acid with respect to octadecylamine.

Example 4
[Ionic liquid 4]
As shown in Table 2, methanesulfonic acid (CH ₃ SO ₃ H, pKa = −2) was used as the Bronsted acid, and octadecylamine (pKa having a linear hydrocarbon group having 18 carbon atoms as the Bronsted base. = 10.7) was used. The difference (ΔpKa) between pKa of Bronsted acid and pKa of Bronsted base was 12.7. An ionic liquid 4 was synthesized by mixing and neutralizing an equivalent amount of trifluoromethanesulfonic acid with respect to octadecylamine.

(Comparative Example 1)
[Comparison ionic liquid 1]
As shown in Table 2, trifluoroacetic acid (CF ₃ COOH, pKa = 0.5) was used as the Bronsted acid, and octadecylamine (pKa = having a linear hydrocarbon group having 18 carbon atoms as the Bronsted base). 10.7) was used. The difference (ΔpKa) between pKa of Bronsted acid and pKa of Bronsted base was 10.2. Comparative ionic liquid 1 was synthesized by mixing octadecylamine with an equivalent amount of trifluoroacetic acid for neutralization.

(Comparative Example 2)
[Comparison ionic liquid 2]
As shown in Table 2, perfluorooctanoic acid (C ₇ F ₁₅ COOH, pKa = 2.5) was used as the Bronsted acid, and octadecylamine having a linear hydrocarbon group having 18 carbon atoms as the Bronsted base. (PKa = 10.7) was used. The difference (ΔpKa) between pKa of Bronsted acid and pKa of Bronsted base was 8.2. Comparative ionic liquid 2 was synthesized by mixing octadecylamine with an equivalent amount of perfluorooctanoic acid for neutralization.

(Comparative Example 3)
[Comparison ionic liquid 3]
As shown in Table 2, stearic acid (C ₁₇ F ₃₅ COOH, pKa = 5.0) was used as the Bronsted acid, and octadecylamine (pKa having a linear hydrocarbon group having 18 carbon atoms as the Bronsted base. = 10.7) was used. The difference (ΔpKa) between pKa of Bronsted acid and pKa of Bronsted base was 5.7. Comparative ionic liquid 3 was synthesized by mixing octadecylamine with an equivalent amount of stearic acid for neutralization.

(Example 5)
Using the lubricant containing the ionic liquid 1, the magnetic disk described above was produced. As shown in Table 3, the CSS measurement of the magnetic disk exceeded 50,000 times, and the CSS measurement after the heating test also exceeded 50,000 times, indicating excellent durability.

(Example 6)
Using the lubricant containing the ionic liquid 2, the magnetic disk described above was produced. As shown in Table 3, the CSS measurement of the magnetic disk exceeded 50,000 times, and the CSS measurement after the heating test also exceeded 50,000 times, indicating excellent durability.

(Example 7)
Using the lubricant containing the ionic liquid 3, the magnetic disk described above was produced. As shown in Table 3, the CSS measurement of the magnetic disk exceeded 50,000 times, and the CSS measurement after the heating test also exceeded 50,000 times, indicating excellent durability.

(Example 8)
Using the lubricant containing the ionic liquid 4, the magnetic disk described above was produced. As shown in Table 3, the CSS measurement of the magnetic disk exceeded 50,000 times, and the CSS measurement after the heating test also exceeded 50,000 times, indicating excellent durability.

(Comparative Example 4)
Using the lubricant containing the comparative ionic liquid 1, the magnetic disk described above was produced. As shown in Table 3, although the CSS measurement of the magnetic disk exceeded 50,000 times, the CSS measurement after the heating test was 1,230 times, and the durability deteriorated by the heating test. This is presumably because the dissociation of ions progressed due to high temperature and the thermal stability deteriorated.

(Comparative Example 5)
Using the lubricant containing the comparative ionic liquid 2, the magnetic disk described above was produced. As shown in Table 3, although the CSS measurement of the magnetic disk exceeded 50,000 times, the CSS measurement after the heating test was 891 times, and the durability deteriorated by the heating test. This is considered to be because, as in Comparative Example 4, the dissociation of ions proceeds at a high temperature and the thermal stability deteriorates.

(Comparative Example 6)
Using the lubricant containing the comparative ionic liquid 3, the magnetic disk described above was produced. As shown in Table 3, although the CSS measurement of the magnetic disk exceeded 50,000 times, the CSS measurement after the heating test was 803 times, and the durability deteriorated by the heating test. This is thought to be because, as in Comparative Example 4, the dissociation of ions progressed at a high temperature and the thermal stability deteriorated.

  Next, an example in which the ionic liquids 1 to 4 and the comparative ionic liquids 1 to 3 are applied to a magnetic tape is shown.

Example 9
The magnetic tape described above was produced using a lubricant containing ionic liquid 1. As shown in Table 4, the coefficient of friction of the magnetic tape after 100 shuttle runs was 0.19 under the environment of temperature -5 ° C, and 0.23 under the environment of temperature 40 ° C and relative humidity 90%. there were. The still durability test was more than 60 minutes in an environment at a temperature of −5 ° C., and more than 60 minutes in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. Further, the still durability test after the heating test was more than 60 min in an environment at a temperature of −5 ° C., and more than 60 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test after the heating test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the ionic liquid 1 has excellent friction characteristics, still durability, and shuttle durability.

(Example 10)
The magnetic tape described above was produced using a lubricant containing ionic liquid 2. As shown in Table 4, the coefficient of friction of the magnetic tape after 100 shuttle runs is 0.20 in an environment at a temperature of −5 ° C., and 0.23 in an environment at a temperature of 40 ° C. and a relative humidity of 90%. there were. The still durability test was more than 60 minutes in an environment at a temperature of −5 ° C., and more than 60 minutes in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. Further, the still durability test after the heating test was more than 60 min in an environment at a temperature of −5 ° C., and more than 60 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test after the heating test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the ionic liquid 2 has excellent friction characteristics, still durability, and shuttle durability.

(Example 11)
Using the lubricant containing the ionic liquid 3, the magnetic tape described above was produced. As shown in Table 4, the coefficient of friction of the magnetic tape after 100 shuttle runs is 0.25 in an environment at a temperature of −5 ° C., and 0.28 in an environment at a temperature of 40 ° C. and a relative humidity of 90%. there were. The still durability test was more than 60 minutes in an environment at a temperature of −5 ° C., and more than 60 minutes in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. Further, the still durability test after the heating test was more than 60 min in an environment at a temperature of −5 ° C., and more than 60 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test after the heating test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the ionic liquid 3 has excellent friction characteristics, still durability, and shuttle durability.

(Example 12)
Using the lubricant containing the ionic liquid 4, the magnetic tape described above was produced. As shown in Table 4, the coefficient of friction of the magnetic tape after 100 shuttle runs is 0.24 in an environment at a temperature of −5 ° C., and 0.28 in an environment at a temperature of 40 ° C. and a relative humidity of 90%. there were. The still durability test was more than 60 minutes in an environment at a temperature of −5 ° C., and more than 60 minutes in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. Further, the still durability test after the heating test was more than 60 min in an environment at a temperature of −5 ° C., and more than 60 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test after the heating test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the ionic liquid 4 has excellent friction characteristics, still durability, and shuttle durability.

(Comparative Example 7)
Using the lubricant containing the comparative ionic liquid 1, the magnetic tape described above was produced. As shown in Table 4, the friction coefficient of the magnetic tape after 100 shuttle runs was 0.23 under the temperature of -5 ° C, and 0.30 under the temperature of 40 ° C and the relative humidity of 90%. there were. The still durability test was 45 min in an environment at a temperature of −5 ° C., and 59 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was 135 times in an environment at a temperature of −5 ° C. and 126 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. Further, the still durability test after the heating test was 26 min in an environment at a temperature of −5 ° C. and 31 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. Further, the shuttle durability test after the heating test was 55 times in an environment at a temperature of −5 ° C. and 42 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the comparative ionic liquid 1 was greatly deteriorated in the still durability and the shuttle durability after the heating test.

(Comparative Example 8)
Using the lubricant containing the comparative ionic liquid 2, the magnetic tape described above was produced. As shown in Table 4, the coefficient of friction of the magnetic tape after 100 shuttle runs was 0.21 under the temperature of -5 ° C, and 0.25 under the temperature of 40 ° C and the relative humidity of 90%. there were. The still durability test was more than 60 minutes in an environment at a temperature of −5 ° C., and more than 60 minutes in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. Further, the still durability test after the heating test was 12 min in an environment at a temperature of −5 ° C., and 16 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. Further, the shuttle durability test after the heating test was 30 times in an environment at a temperature of −5 ° C. and 23 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the comparative ionic liquid 2 was greatly deteriorated in the still durability after the heating test and the shuttle durability.

(Comparative Example 9)
Using the lubricant containing the comparative ionic liquid 3, the magnetic tape described above was produced. As shown in Table 4, the coefficient of friction of the magnetic tape after 100 shuttle runs was 0.21 under the temperature of -5 ° C, and 0.25 under the temperature of 40 ° C and the relative humidity of 90%. there were. The still durability test was more than 60 minutes in an environment at a temperature of −5 ° C., and more than 60 minutes in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. Further, the still durability test after the heating test was 7 min in an environment at a temperature of −5 ° C., and 9 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. Further, the shuttle durability test after the heating test was 15 times in an environment at a temperature of −5 ° C., and 12 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the comparative ionic liquid 3 was greatly deteriorated in the still durability after the heating test and the shuttle durability.

  From Tables 3 and 4, it is possible to obtain excellent heat resistance and durability by using an ionic liquid in which the difference between the pKa of Bronsted acid in water and the pKa of Bronsted base in water (ΔpKa) is 12 or more. I understood that I could do it.

<3.2 Effect of carbon number and structure of linear hydrocarbon of Bronsted base>
Next, an ionic liquid was synthesized using aliphatic amines having different carbon numbers and structures (double bonds, partially branched) of linear hydrocarbons as Bronsted bases. Then, a lubricant containing an ionic liquid was used for the magnetic recording medium, and the influence of the carbon number and structure of the linear hydrocarbon of the Bronsted base was investigated. The Bronsted basicity of the aliphatic amine did not vary greatly with the length of the hydrocarbon, and the difference (ΔpKa) between the pKa of the Bronsted acid and the BrKasted base was approximately 17-18.

(Example 13)
[Ionic liquid 5]
As shown in Table 5, decylamine (C ₁₀ H ₂₁ NH ₂₎ having a straight-chain hydrocarbon group having 10 carbon atoms as a Bronsted base, using trifluoromethanesulfonic acid (CF ₃ SO ₃ H) as the Bronsted acid. ) Was used. An ionic liquid 5 was synthesized by mixing decylamine with an equivalent amount of trifluoromethanesulfonic acid for neutralization.
(Example 14)

[Ionic liquid 6]
As shown in Table 5, trifluoromethanesulfonic acid (CF ₃ SO ₃ H) was used as the Bronsted acid, and tetradecylamine (C ₁₄ H ₂₉₎ having a C ₁₄ linear hydrocarbon group as the Bronsted base. NH ₂₎ was used. An ionic liquid 6 was synthesized by mixing tetradecylamine with an equivalent amount of trifluoromethanesulfonic acid for neutralization.

(Example 15)
[Ionic liquid 7]
As shown in Table 5, trifluoromethanesulfonic acid (CF ₃ SO ₃ H) was used as the Bronsted acid, and eicosylamine (C ₂₀ H ₄₁ having a C20 linear hydrocarbon group as the Bronsted base). NH ₂₎ was used. Equivalent liquid trifluoromethanesulfonic acid was mixed with eicosylamine and neutralized to synthesize ionic liquid 7.

(Example 16)
[Ionic liquid 8]
As shown in Table 5, oleylamine (C3) having a straight-chain hydrocarbon group having a double bond having 18 carbon atoms as a Bronsted base, using trifluoromethanesulfonic acid (CF ₃ SO ₃ H) as a Bronsted acid. ₁₈ H ₃₅ NH ₂ ) was used. An ionic liquid 8 was synthesized by mixing oleylamine with an equivalent amount of trifluoromethanesulfonic acid for neutralization.

(Example 17)
[Ionic liquid 9]
As shown in Table 5, trifluoromethanesulfonic acid (CF ₃ SO ₃ H) was used as the Bronsted acid, and 2-heptylundecyl having a straight-chain hydrocarbon group having 18 carbon atoms as the Bronsted base. amine _{(CH 3 (CH 2) n} CH (C 7 H 15) -NH 2) was used (having a partially branched). An ionic liquid 9 was synthesized by mixing 2-heptylundecylamine with an equivalent amount of trifluoromethanesulfonic acid for neutralization.

(Comparative Example 10)
[Comparison ionic liquid 4]
As shown in Table 5, octylamine (C ₈ H ₁₇ NH) having a straight-chain hydrocarbon group having 8 carbon atoms as the Bronsted base, using trifluoromethanesulfonic acid (CF ₃ SO ₃ H) as the Bronsted acid. ₂ ) was used. Comparative ionic liquid 4 was synthesized by mixing octylamine with an equivalent amount of trifluoromethanesulfonic acid for neutralization.

(Comparative Example 11)
[Comparison ionic liquid 5]
As shown in Table 5, trifluoromethanesulfonic acid (CF ₃ SO ₃ H) was used as the Bronsted acid, and isobutylamine (C ₄ H ₉ NH ₂ ) having 4 carbon atoms was used as the Bronsted base. Comparative ionic liquid 4 was synthesized by mixing and neutralizing an equivalent amount of trifluoromethanesulfonic acid with respect to isobutylamine.

(Example 18)
The magnetic disk described above was produced using a lubricant containing ionic liquid 5. As shown in Table 6, the CSS measurement of the magnetic disk exceeded 50,000 times and showed excellent durability.

(Example 19)
The magnetic disk described above was manufactured using a lubricant containing ionic liquid 6. As shown in Table 6, the CSS measurement of the magnetic disk exceeded 50,000 times and showed excellent durability.

(Example 20)
The magnetic disk described above was produced using a lubricant containing ionic liquid 7. As shown in Table 6, the CSS measurement of the magnetic disk exceeded 50,000 times and showed excellent durability.

(Example 21)
The magnetic disk described above was produced using a lubricant containing ionic liquid 8. As shown in Table 6, the CSS measurement of the magnetic disk exceeded 50,000 times and showed excellent durability.

(Example 21)
The magnetic disk described above was produced using a lubricant containing ionic liquid 9. As shown in Table 6, the CSS measurement of the magnetic disk exceeded 50,000 times and showed excellent durability.

(Comparative Example 12)
Using the lubricant containing the comparative ionic liquid 4, the above magnetic disk was produced. As shown in Table 6, the CSS measurement of the magnetic disk was 23,500 times.

(Comparative Example 13)
Using the lubricant containing the comparative ionic liquid 5, the magnetic disk described above was produced. As shown in Table 6, the CSS measurement of the magnetic disk was 11,000 times.

  From Table 6, Examples 18-22 which used the ionic liquid formed from the Bronsted base whose hydrocarbon carbon number is at least 10 or more for a magnetic disk had a CSS endurance test exceeding 50,000 times, and carbon It turned out that it has the durability outstanding compared with the comparative examples 12 and 13 using the ionic liquid formed from a Bronsted base whose number is eight or less.

  Next, the example which applied the ionic liquids 5-9 and the comparison ionic liquids 4 and 5 to the magnetic tape is shown.

(Example 23)
The magnetic tape described above was produced using a lubricant containing ionic liquid 5. As shown in Table 7, the friction coefficient of the magnetic tape after 100 shuttle runs was 0.22 under the environment of temperature -5 ° C, and 0.23 under the environment of temperature 40 ° C and relative humidity 90%. there were. The still durability test was 53 min in an environment at a temperature of −5 ° C., and exceeded 60 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. Further, the shuttle durability test was 153 times in an environment at a temperature of −5 ° C. and 126 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the ionic liquid 5 has excellent friction characteristics, still durability, and shuttle durability.

(Example 24)
The magnetic tape described above was produced using a lubricant containing ionic liquid 6. As shown in Table 7, the friction coefficient of the magnetic tape after 100 shuttle runs was 0.20 under the temperature of -5 ° C and 0.21 under the temperature of 40 ° C and the relative humidity of 90%. there were. The still durability test was more than 60 minutes in an environment at a temperature of −5 ° C., and more than 60 minutes in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the ionic liquid 6 has excellent friction characteristics, still durability, and shuttle durability.

(Example 25)
The magnetic tape described above was produced using a lubricant containing ionic liquid 7. As shown in Table 7, the friction coefficient of the magnetic tape after 100 shuttle runs is 0.21 under the environment of temperature -5 ° C, and 0.21 under the environment of temperature 40 ° C and relative humidity 90%. there were. The still durability test was more than 60 minutes in an environment at a temperature of −5 ° C., and more than 60 minutes in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the ionic liquid 7 has excellent friction characteristics, still durability, and shuttle durability.

(Example 26)
The magnetic tape described above was produced using a lubricant containing ionic liquid 8. As shown in Table 7, the friction coefficient of the magnetic tape after 100 shuttle runs was 0.22 under the environment of temperature -5 ° C, and 0.22 under the environment of temperature 40 ° C and relative humidity 90%. there were. The still durability test was more than 60 minutes in an environment at a temperature of −5 ° C., and more than 60 minutes in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the ionic liquid 8 has excellent friction characteristics, still durability, and shuttle durability.

(Example 27)
Using the lubricant containing the ionic liquid 9, the magnetic tape described above was produced. As shown in Table 7, the coefficient of friction of the magnetic tape after 100 shuttle runs is 0.24 under the environment of temperature -5 ° C, and 0.25 under the environment of temperature 40 ° C and relative humidity 90%. there were. The still durability test was 51 min in an environment at a temperature of −5 ° C. and 59 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. In addition, the shuttle durability test was 135 times in an environment at a temperature of −5 ° C. and 158 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the ionic liquid 9 has excellent friction characteristics, still durability, and shuttle durability.

(Comparative Example 14)
Using the lubricant containing the comparative ionic liquid 4, the above magnetic tape was produced. As shown in Table 7, the friction coefficient of the magnetic tape after 100 shuttle runs was 0.29 under the temperature of -5 ° C, and 0.30 under the temperature of 40 ° C and the relative humidity of 90%. there were. The still durability test was 35 min in an environment at a temperature of −5 ° C., and 39 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was 96 times in an environment at a temperature of −5 ° C. and 95 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%.

(Comparative Example 15)
Using the lubricant containing the comparative ionic liquid 5, the magnetic tape described above was produced. As shown in Table 7, the friction coefficient of the magnetic tape after 100 shuttle runs was 0.36 under the temperature of -5 ° C, and 0.41 under the temperature of 40 ° C and the relative humidity of 90%. there were. The still durability test was 15 minutes in an environment at a temperature of −5 ° C., and 25 minutes in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was 86 times in an environment at a temperature of −5 ° C. and 54 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%.

  From Table 7, Examples 23-27 which used the ionic liquid formed from the Bronsted base whose hydrocarbon carbon number is at least 10 or more for the magnetic tape are formed from the Bronsted base whose carbon number is 8 or less. It was found that the coefficient of friction, the still durability, and the shuttle durability were greatly improved as compared with Comparative Examples 14 and 15 using an ionic liquid. Further, in Examples 26 and 27 in which an ionic liquid in which a double bond is introduced into a linear hydrocarbon group or an ionic liquid having a branched hydrocarbon group is used for a magnetic tape, compared with those having 14 or more carbon atoms. Although the coefficient of friction slightly increased, the actual specifications of still durability and shuttle durability were sufficiently satisfied.

<3.3 Influence of structure other than hydrocarbon group of Bronsted base>
Next, as a Bronsted base, an ionic liquid was synthesized using a compound (cyclic amidine) whose structure other than the hydrocarbon group is different from that of the amine. Then, a lubricant containing an ionic liquid was used for the magnetic recording medium, and the influence of the structure other than the hydrocarbon group of the Bronsted base was examined.

(Example 28)
_<C 8 _F 17 _SO ³ - Synthesis of ^{_{H 3 N + C 18 H 37}} ( ionic liquid 10)>
Stearylamine was dissolved in a mixed solvent of 85% by mass of n-hexane / 15% by mass of ethanol, equimolar perfluorooctanesulfonic acid dissolved in ethanol was added, and the mixture was heated at 60 ° C. for 30 minutes. After removing the solvent, n- recrystallized from a small amount of ethanol were mixed solvent of hexane, colorless crystals _- to give the ^{_{(C 8 F 17 SO 3 H}} 3 N + C 18 H 37).

(Example 29)
<Synthesis of 6-pentadecyldiazabicycloundecene (6-Pentadecyl-1,8-diazabicclo [5.4.0] undec-7-ene: 6-pentadecyl DBU)>
6-pentadecyldiazabicycloundecene represented by the following structural formula (1) is described in Matsumura et al. (N. Matsumura, H. Nishiguchi, M. Okada, and S. Yoneda, J. Heterocyclic Chem. 885-887, Vol / 23. Issue 3 (1986)).

<Synthesis of ionic liquid 11>
The compound represented by the structural formula (1) obtained by the above method was dissolved in a mixed solvent of 85% by mass of n-hexane / 15% by mass of ethanol. Thereto was added perfluorooctanesulfonic acid [95 mol% with respect to the compound represented by the structural formula (1)] dissolved in ethanol. After removing the solvent, the compound was washed with n-hexane to remove an excess of the compound represented by the structural formula (1), whereby an ionic liquid 11 was obtained.

(Comparative Example 16)
_<C 7 _F 15 ^COO - Synthesis of ^{_{H 3 N + C 18 H 37}} ( Comparative ionic liquid 6)>
Tribology Trans, Vol. 37, no. 1 (Jan. 1994), pp. Synthesized according to 99-105.

(Comparative Example 17)
^{_{<C 7 F 15 CH 2 O}} - Synthesis of _{^{H 3 N + C 18 H 37}} ( Comparative ionic liquid 7)>
Stearylamine and equimolar pentadecafluorooctanol were dissolved in a solvent in which n-hexane and a small amount of ethanol were mixed, and heated at 60 ° C. for 30 minutes. Filtration and removal of dust and the like followed by recrystallization gave colorless crystals.

  Table 8 shows the BrKasted acid pKa, Brönsted base pKa and ΔpKa of the ionic liquids obtained in Examples 28 and 29 and Comparative Examples 16 and 17.

<Thermal analysis results>
Seiko Instruments Inc. TG measurement of the ionic liquids obtained in Examples 2, 28 and 29 and Comparative Examples 16 and 17 was performed using EXSTAR 6000 (Examples 30 and 31, Comparative Examples 18 and 19). Moreover, TG measurement was also performed on Z-DOL (Comparative Example 20). While purging air, weight loss was measured in a temperature range of 30 ° C. to 600 ° C. at a temperature rising rate of 10 ° C./min. The results are shown in FIG. The 10% weight loss temperatures are summarized in Table 9 below.
In addition, the exothermic peak temperature in the differential thermal analysis (DTA) measurement of the ionic liquid 2 was 374 degreeC and 380 degreeC. The exothermic peak temperatures in differential thermal analysis (DTA) measurement of the ionic liquid 10 were 383 ° C. and 402 ° C.

  From this result, it was found that the ionic liquids 10 and 11 with ΔpKa greatly exceeding 7 had a very high 10% weight loss temperature, and in particular, the latter was higher by 200 ° C. or more than Z-DOL. In the ionic liquid 11, by changing the Bronsted base from stearylamine to a DBU derivative having high base strength, ΔpKa increased and the 10% weight loss temperature increased by 45 ° C. In contrast, the comparative ionic liquid 6 having a ΔpKa of 6.9 has a poor heat resistance, such that the 10% weight reduction temperature is 205 ° C. and the comparative ionic liquid 7 having a ΔpKa of 4 or less has a 10% weight reduction temperature of 62 ° C. I understood.

(Examples 32-33, Comparative Examples 21-23)
Next, an embodiment applied to a metal thin film type magnetic recording medium (magnetic disk) will be described.
Using the lubricant containing the ionic liquid shown in Table 10, the magnetic disk described above was produced. Using the produced magnetic disk, a CSS durability test and a CSS durability test after heating were performed. The results are shown in Table 10.

  From Table 10, in Examples 32 and 33, a carbon protective film is formed on the surface of the metal magnetic thin film, and a Bronsted acid and a Bronsted base containing a linear hydrocarbon group having 10 or more carbon atoms are formed on the carbon protective film. Each sample disk using a compound having a ΔpKa of 12 or more as a lubricant is excellent in CSS characteristics and improved in durability, and the characteristics are affected even after heating. It was. When ΔpKa is smaller than 10, durability after heating is deteriorated, but this is considered to be caused by deterioration of thermal stability due to dissociation and decomposition of ions at a high temperature.

(Examples 34-35, Comparative Examples 24-26)
Next, an embodiment applied to a magnetic tape will be described.
Using the lubricant containing the ionic liquid shown in Table 11, the magnetic tape described above was produced. Using the produced magnetic tape, a friction coefficient, a still durability test, a shuttle durability test, a still durability test after heating, and a shuttle durability test after heating were performed after 100 times of shuttle travel. The results are shown in Table 11.

  These results are also an ionic liquid of Bronsted acid and a Bronsted base containing a linear hydrocarbon group having 10 or more carbon atoms, and a magnetic tape coated with a compound having a ΔpKa of 12 or more as a lubricant. Excellent wear resistance, still durability, shuttle durability. However, the compound with ΔpKa of 7 or less shown as a comparative example had a great deterioration in durability after heating, as in the case of the above-mentioned disk.

(Example 36)
[Ionic liquid 12]
<Synthesis of n-octadecylamine-bistrifluoromethanesulfonylimide salt>
A synthesis scheme is shown below.

  For the synthesis of n-octadecylamine-bisnonafluorobutanesulfonylimide salt, reference was made to the following Huang et al. literature (non-patent literature: ing-Fang Huang, Huimin Luo, Chengdu Liang, I-Wen Sun, Gary A. et al. Baker, and Shen Dai, “Hydrophobic Bronshed Acid-Base Ionic Liquids Based on PAMAM Dendrimers with High Plu.

First, 15.18 g of n-octadecylamine was dissolved in ethanol, 60% concentrated nitric acid (d = 1.360) was added dropwise with stirring, and the addition was terminated when the neutralization point was reached. After cooling, the precipitated crystals were filtered and dried to obtain n-octadecylamine nitrate.
Next, 6.80 g of n-octadecylamine nitrate was dissolved in ethanol, and 5.91 g of bistrifluoromethanesulfimidolithium salt dissolved in ethanol was added dropwise while stirring. Heated to reflux for hours. After cooling, the solvent was removed, water and diethyl ether were added, the organic layer was separated, and the organic layer was further washed with water. The organic layer was dried over anhydrous magnesium sulfate, the solvent was removed, and recrystallization was performed with n-hexane to obtain colorless crystals of n-octadecylamine-bistrifluoromethanesulfonylimide salt having a melting point of 67 ° C. The FTIR spectrum and TG / DTA are shown in FIGS.

In this example, FTIR was measured by a transmission method using a KBr plate method or a KBr tablet method using FT / IR-460 manufactured by JASCO Corporation. The resolution at that time is 4 cm ⁻¹ .
In addition, in the TG / DTA measurement, an EXSTAR6000 manufactured by Seiko Instruments Inc. is used, and air is introduced at a flow rate of 200 mL / min. Measurements were made. As an apparatus for gas chromatography mass spectrum, Agilent 6890/5975 MSD was used. The column was DB-1 (15 m, diameter 0.25 mm, film thickness 0.1 μm), the injection temperature was 280 ° C., the initial column temperature was held at 40 ° C. for 5 minutes, and then the heating rate was 20 ° C./min to 340 ° C. The temperature was raised and held at that temperature. The mass unit was 5975 MSD, the MS detection method was EI ⁺ , the quadrupole temperature was 150 ° C., the ion source temperature was 300 ° C., the mass scan range was m / z 33-700, and the calibration was PFTBA.

Table 12 shows the absorption wave number of IR and its attribution. S-N-S bond of a symmetric stretching vibration 1,038cm ^-1, symmetric stretching vibration of SO ₂ bind to 1,131cm ^-1, symmetric stretching vibration of CF ₃ to 1,194cm ^-1, the 1,344Cm ^-1 antisymmetric stretching vibration of SO ₂ bond, _NH ^{4 +} antisymmetric bending vibration of the 1,600cm ^-1, symmetric stretching vibration of CH ₂ in 2,850cm ^-1, antisymmetric stretch of CH ₂ in 2,916Cm ^-1 The structure was determined from the fact that a broad NH ₄ ⁺ symmetrical stretching vibration was observed in the vibration, 3,360 cm ⁻¹ -3, 020 cm ⁻¹ .
From TG / DTA, the 10% weight loss temperature is very high at 329 ° C., and the weight loss is exothermic, suggesting that the weight loss is caused by the decomposition reaction of the compound.

(Example 37)
[Ionic liquid 13]
<Synthesis of n-octadecylamine-bisnonafluorobutanesulfonylimide salt>
A synthesis scheme is shown below.

  9.31 g of bisnonafluorobutanesulfonylimide was dissolved in ethanol, n-octadecylamine dissolved in ethanol was added, and the mixture was heated to reflux for 30 minutes, and then the solvent was removed. Recrystallization from n-hexane gave colorless crystals of n-octadecylamine-bisnonafluorobutanesulfonylimide salt having a melting point of 118 ° C. The FTIR spectrum and TG / DTA are shown in FIGS.

Table 13 shows the absorption wave number of IR and its attribution. S-N-S bond of a symmetric stretching vibration 1,031cm ^-1, symmetric stretching vibration of SO ₂ bind to 1,088cm ^-1, the 1,200Cm ^-1 and 1,141Cm ^-1 of CF ₃ and CF ₂ symmetry stretching vibration, antisymmetric stretching vibration of SO ₂ bind to 1,355cm ^-1, _NH ^{4 +} antisymmetric bending vibration of the 1,616Cm ^-1, symmetric stretching vibration of CH ₂ in 2,856cm ^-1, 2,926cm ^-1 antisymmetric stretching vibration of CH ^_2, since the symmetric stretching vibration of broad _NH ^{4 +} is seen to 3,360cm ^-1 -3,025cm -1, its structure has been determined.
Also, from TG / DTA, the 10% weight loss temperature is very high at 331 ° C. Also in this case, the weight loss is exothermic, suggesting that the weight loss is due to the decomposition reaction of the compound. .

(Example 38)
[Ionic liquid 14]
<Synthesis of n-octadecylamine-cyclo-hexafluoropropane-1,3-bis (sulfonyl) imide salt>
A synthesis scheme is shown below.

  In ethanol, 5.45 g of cyclo-hexafluoropropane-1,3-bis (sulfonyl) imide was dissolved, and 5 g of n-octadecylamine dissolved in ethanol was added. Since there was an exotherm, the surroundings were cooled with ice. The solvent was removed after 30 minutes of heating under reflux. Recrystallization from n-hexane gave colorless crystals of n-octadecylamine-cyclo-hexafluoropropane-1,3-bis (sulfonyl) imide salt having a melting point of 92 ° C. The FTIR spectrum and TG / DTA are shown in FIG. 9 and FIG.

Table 14 shows the absorption wave number of IR and its attribution. S-N-S bond of a symmetric stretching vibration 1,043cm ^-1, symmetric stretching vibration of SO ₂ bind to 1,096cm ^-1, symmetric stretching vibration of _{F 2} to 1,188Cm ^-1 and 1,154cm ^{-1, 1} 348 cm ⁻¹ , SO ₂ bond reverse symmetric stretching vibration, 1,608 cm ⁻¹ NH ₄ ⁺ reverse symmetric bending vibration, 2,850 cm ⁻¹ CH ₂ symmetric stretching vibration, 2,920 cm ⁻¹ The structure was determined from the inverse symmetrical stretching vibration of CH ₂ and the broad symmetrical stretching vibration of NH ₄ ⁺ at 3,350 cm ⁻¹ -3,035 cm ⁻¹ .
Also, from TG / DTA, the 10% weight loss temperature is very high at 347 ° C. Also in this case, the weight loss is exothermic, suggesting that the weight loss is caused by the decomposition reaction of the compound. .

(Example 39)
[Ionic liquid 15]
<Synthesis of 6-n-octadecyl-1,8-diazabicyclo [5.4.0] -7-undecene (C18-DBU) pentadecafluorooctane sulfonate>
A synthesis scheme of C18-DBU is shown below.

  C18-DBU is the method of Matsumura et al. -Ene, "J. Heterocyclic Chemistry Vol. 23, Issue 3, pp. 885-887 (1986)).

  First, 7.17 g of raw material 1,8-diazabiccyclo [5.4.0] -7-undecene (DBU) was dissolved in a tetrahydrofuran (THF) solution and cooled to 0 ° C., and the n concentration having a concentration of 1.64 mol / L was obtained. -29 cc of butyl lithium was added dropwise under an argon gas atmosphere, and the mixture was stirred at 0 ° C for 1 hour. A solution prepared by dissolving 15.71 g of octadecyl bromide in THF was added dropwise to the solution, and the mixture was left to stir for 24 hours. The THF was immediately used after being dried with type 4A molecular sieves and purified by distillation. Then, after acidifying with hydrochloric acid, the solvent was removed, and the product dissolved in hexane was purified by column chromatography on aminated silica gel to obtain a colorless crystal product. Yield 90%.

About this product, it confirmed that the target C18-DBU was synthesize | combined by the gas chromatography and the mass spectrum.
In addition, the peak of 17 minutes of outflow time of gas chromatography was 99.5% in area ratio.

Next, a synthesis scheme of C18-DBU pentadecafluorooctane sulfonate is shown below.

After dissolving 3.00 g of C18-DBU and 3.71 g of heptadecafluorooctane sulfonic acid (C ₈ F ₁₇ SO ₃ H) in ethanol, the solvent was removed, and recrystallization from an n-hexane / ethanol mixed solvent was colorless. Crystals were obtained. Melting point is 41 ° C.

The results of FTIR and TG / DTA are shown in FIGS. 11 and 12, respectively.
Table 15 shows the absorption wave number of IR and its attribution. Symmetric stretching vibration of CF ₃ and CF ₂ in the vicinity of 1,252cm ^-1, stretching vibration of C = N to 1,643cm ^-1, symmetric stretching vibration of CH ₂ in 2,851cm ^-1, CH in 2,920Cm ^-1 The structure was determined from the presence of ₂ inversely symmetric stretching vibrations and broad NH ⁺ symmetric stretching vibrations at 3,410 cm ⁻¹ -3 and 178 cm ⁻¹ .
Also, from TG / DTA, the 10% weight loss temperature is as high as 384 ° C. Also in this case, the weight loss is exothermic, suggesting that the weight loss is caused by the decomposition reaction of the compound.

(Example 40)
[Ionic liquid 16]
<Synthesis of C18-DBU cyclo-hexafluoropropane-1,3-bis (sulfonyl) imide salt>
A synthesis scheme of C18-DBU cyclo-hexafluoropropane-1,3-bis (sulfonyl) imide salt is shown below.

C18-DBU (3.00 g) synthesized in the same manner as in Example 39 and 2.18 g of cyclo-hexafluoropropane-1,3-bis (sulfonyl) imide were dissolved in ethanol, heated to reflux for 30 min, the solvent was removed, and n- Recrystallization from hexane gave colorless crystals. Melting point 52 ° C.
The results of FTIR and TG / DTA are shown in FIGS. 13 and 14, respectively.

Table 16 shows the absorption wave number of IR and its attribution. S-N-S bond of a symmetric stretching vibration 1,042cm ^-1, symmetric stretching vibration of SO ₂ bind to 1,091cm ^-1, symmetric stretching vibration of CF ₂ to 1,164cm ^-1, the 1,360Cm ^-1 antisymmetric stretching vibration of SO ₂ bond stretching vibration of the 1,633cm ^-1 C = N, symmetric stretching vibration of CH ₂ in 2,848Cm ^-1, antisymmetric stretching vibration of CH ₂ in 2,920cm ^-1, 3 , 387 cm ⁻¹ , a symmetrical stretching vibration of NH ⁺ was observed, and the structure was determined.
Also, from TG / DTA, the 10% weight loss temperature is as high as 386 ° C. Also in this case, the weight loss is exothermic, suggesting that the weight loss is due to the decomposition reaction of the compound.

(Example 41)
[Ionic liquid 17]
<Synthesis of 7-n-octadecyl-1,5,7-triazabicyclo [4.4.0] -5-decene (C18-TBD) pentadecafluorooctane sulfonate>
First, a synthesis scheme of the raw material 7-n-octadecyl-1,5,7-triazabicyclo [4.4.0] -5-decene (C18-TBD) is shown below.

  R. W. (Non-patent literature: Roger W. Alder, Rodney W. Mowlam, David J. Vachon and Gray R. Weisman, “New Synthetic Routes to Macrocycle. Chem. Commun. Pp. 507-508 (1992)).

  That is, 1,5,7-triazabicyclo [4.4.0] -5-decene (TBD) in which sodium hydride (55% by mass hexane) was dissolved in dry THF prepared in the same manner as in Example 39. ) Added to 8.72 g at 10 ° C. and stirred. While maintaining the temperature at 10 ° C., brominated octadecane was added dropwise over 20 minutes, and the mixture was stirred for 30 minutes at room temperature for 2 hours and then heated to reflux for 1 hour. The temperature was returned to room temperature, and excess sodium hydride was reacted with ethanol. After removing the solvent, column chromatography was performed on silica gel that had been amino-treated to obtain a pale yellow target product.

About this product, it confirmed that the target C18-TBD (molecular weight 391) was synthesize | combined by the gas chromatography and the mass spectrum.
In gas chromatography, impurities in the solvent were observed at 10.5 minutes, but the peak at the outflow time of 17 minutes was 98% in area ratio.

Next, a synthesis scheme of C18-TBD pentadecafluorooctane sulfonate is shown below.

3.91 g of C18-TBD and 5.00 g of pentadecafluorooctane sulfonic acid were dissolved in ethanol, heated for 30 minutes under reflux, and then the solvent was removed. Recrystallization from n-hexane gave colorless crystals. Melting point 65 ° C.
IR and TG / DTA are shown in FIGS.

Table 17 shows the absorption wave number of IR and its attribution. Symmetric stretching vibration of CF ₃ and CF ₂ in the vicinity of 1,255cm ^-1, stretching vibration of C = N to 1,602cm ^-1, symmetric stretching vibration of CH ₂ in 2,851cm ^-1, CH in 2,924Cm ^-1 The structure was determined from the presence of ₂ inversely symmetric stretching vibrations, and NH ⁺ symmetric stretching vibrations at 3,289 cm ⁻¹ .
Also, from TG / DTA, the 10% weight loss temperature is as high as 381 ° C. Also in this case, the weight loss is exothermic, suggesting that the weight loss is caused by the decomposition reaction of the compound.

(Example 42)
[Ionic liquid 18]
<Synthesis of C18-TBD cyclo-hexafluoropropane-1,3-bis (sulfonyl) imide salt>
A synthesis scheme of C18-TBD cyclo-hexafluoropropane-1,3-bis (sulfonyl) imide salt is shown below.

C18-TBD (4.00 g) synthesized in the same manner as in Example 41 and hexafluoropropanesulfonylimide (3.00 g) were dissolved in ethanol. After heating at reflux for 30 minutes, the solvent was removed, followed by re-use with a mixed solvent of n-hexane / ethanol. Crystallization was performed. Colorless crystals, mp 67 ° C.
The results of FTIR and TG / DTA are shown in FIGS. 17 and 18, respectively.

Table 18 summarizes the absorption wave number of IR and its attribution. S-N-S bond of a symmetric stretching vibration 1,042cm ^-1, symmetric stretching vibration of SO ₂ bind to 1,092cm ^-1, symmetric stretching vibration of CF ₂ to 1,157cm ^-1, the 1,361Cm ^-1 antisymmetric stretching vibration of SO ₂ bond stretching vibration of the 1,628cm ^-1 C = N, symmetric stretching vibration of CH ₂ in 2,849Cm ^-1, antisymmetric stretching vibration of CH ₂ in 2,921cm ^-1, 3 , 412 cm ⁻¹ , a symmetrical stretching vibration of NH ⁺ is observed, so that the structure was determined.
Also, from TG / DTA, the 10% weight loss temperature is as high as 380 ° C. Also in this case, the weight loss is exothermic, suggesting that the weight loss is caused by the decomposition reaction of the compound.

(Comparative Example 27)
[Comparison ionic liquid 8]
<Synthesis of DBU pentadecafluorooctane sulfonate>
A synthesis scheme of DBU pentadecafluorooctane sulfonate is shown below.

About DBU, what was purchased from Tokyo Chemical Industry Co., Ltd. was used as it was, without refine | purifying. DBU (5.00 g) and pentadecafluorooctanesulfonic acid (1.52 g) were dissolved in ethanol, and the solvent was removed after heating at reflux for 30 min. Subsequently, recrystallization was performed with an n-hexane / ethanol mixed solvent. Colorless crystals, mp 121 ° C.
The results of FTIR and TG / DTA are shown in FIGS. 19 and 20, respectively.

Table 19 shows the absorption wave number of IR and its attribution. Symmetric stretching vibration of CF ₃ and CF ₂ in the vicinity of 1,282cm ^-1, stretching vibration of C = N to 1,651cm ^-1, symmetric stretching vibration of CH ₂ in 2,868cm ^-1, CH in 2,943Cm ^-1 The structure was determined from the presence of ₂ inversely symmetric stretching vibrations and broad NH ⁺ symmetric stretching vibrations at 3,289 cm ⁻¹ .
Also, from TG / DTA, the 10% weight loss temperature is as high as 393 ° C. Also in this case, the weight loss is exothermic, suggesting that the weight loss is caused by the decomposition reaction of the compound.

(Comparative Example 28)
[Comparison ionic liquid 9]
<Synthesis of TBD pentadecafluorosulfonate>
About TBD, what was purchased from Tokyo Chemical Industry Co., Ltd. was used without purification. A synthesis scheme of TBD pentadecafluorooctane sulfonate is shown below.

1.50 g of TBD and 5.39 g of pentadecafluorooctane sulfonic acid were dissolved in ethanol, heated for 30 minutes under reflux, and then the solvent was removed. Recrystallization from n-hexane gave colorless crystals. Mp 84 ° C.
FTIR and TG / DTA are shown in FIGS.

Table 20 shows the absorption wave number of IR and its attribution. 1,202 and symmetric stretching vibration of CF ₃ and CF ₂ in 1,247cm ^-1, stretching vibration of C = N to 1,633cm ^-1, symmetric stretching vibration of CH ₂ in 2,876cm ^-1, 2,933cm ^{- 1} to antisymmetric stretching vibration of CH ^_2, since the symmetric stretching vibration of NH ⁺ is seen to 3,040cm ^-1 -3,629cm -1, its structure has been determined.
TG / DTA indicates that the 10% weight loss temperature is as high as 371 ° C., and in this case, the weight loss is exothermic, suggesting that the weight loss is caused by the decomposition reaction of the compound.

  The synthesized ionic liquid is summarized in Table 21 below.

The ionic liquids synthesized in Examples 36 to 42 are referred to as ionic liquids 12 to 18. The ionic liquids synthesized in Comparative Examples 27 to 28 are referred to as Comparative ionic liquids 8 to 9. The 10% weight loss temperature at that time is also shown.
Since the ionic liquids synthesized here including the comparative ionic liquid have ΔpKa between the acid and the base of 12 or more, the decomposition temperature is high, and the 10% weight loss temperature is all 320 ° C. or more.

(Example 43)
The magnetic disk described above was produced using a lubricant containing n-octadecylamine-bistrifluoromethanesulfonylimide salt which is [Ionic liquid 12]. As shown in Table 23, the CSS measurement of the magnetic disk exceeded 50,000 times, and the CSS measurement after the heating test exceeded 50,000 times, indicating excellent durability.

(Example 44)
The magnetic disk described above was prepared using a lubricant containing n-octadecylamine-bisnonafluorobutanesulfonylimide salt which is [Ionic Liquid 13]. As shown in Table 23, the CSS measurement of the magnetic disk exceeded 50,000 times, and the CSS measurement after the heating test exceeded 50,000 times, indicating excellent durability.

(Example 45)
The magnetic disk described above was produced using a lubricant containing n-octadecylamine-cyclo-hexafluoropropane-1,3-bis (sulfonyl) imide salt which is [Ionic Liquid 14]. As shown in Table 23, the CSS measurement of the magnetic disk exceeded 50,000 times, and the CSS measurement after the heating test exceeded 50,000 times, indicating excellent durability.

(Example 46)
The magnetic disk described above was produced using a lubricant containing C18-DBU pentadecafluorooctane sulfonate which is [Ionic liquid 15]. As shown in Table 23, the CSS measurement of the magnetic disk exceeded 50,000 times, and the CSS measurement after the heating test exceeded 50,000 times, indicating excellent durability.

(Example 47)
The magnetic disk described above was produced using a lubricant containing C18-DBU cyclo-hexafluoropropane-1,3-bis (sulfonyl) imide salt which is [Ionic liquid 16]. As shown in Table 23, the CSS measurement of the magnetic disk exceeded 50,000 times, and the CSS measurement after the heating test exceeded 50,000 times, indicating excellent durability.

(Example 48)
The magnetic disk described above was manufactured using a lubricant containing C18-TBD pentadecafluorooctane sulfonate, which is [Ionic Liquid 17]. As shown in Table 23, the CSS measurement of the magnetic disk exceeded 50,000 times, and the CSS measurement after the heating test exceeded 50,000 times, indicating excellent durability.

(Example 49)
Using the lubricant containing C18-TBD cyclo-hexafluoropropane-1,3-bis (sulfonyl) imide salt which is [Ionic liquid 18], the magnetic disk described above was produced. As shown in Table 23, the CSS measurement of the magnetic disk exceeded 50,000 times, and the CSS measurement after the heating test exceeded 50,000 times, indicating excellent durability.

(Comparative Example 29)
Using the lubricant containing DBU pentadecafluorooctane sulfonate which is [Comparative Ionic Liquid 8], the magnetic disk described above was produced. As shown in Table 23, the durability of the magnetic disk in the CSS measurement is 5,860 times, the CSS measurement after the heating test is 14,230 times, and long-chain hydrocarbons are not included in the lubricant. It is thought that the friction coefficient increased.

(Comparative Example 30)
Using the lubricant containing TBD pentadecafluorooctane sulfonate which is [Comparative Ionic Liquid 9], the above magnetic disk was produced. As shown in Table 23, the durability of the magnetic disk in the CSS measurement is 6,230 times, the CSS measurement after the heating test is 18,501 times, and long-chain hydrocarbons are not included in the lubricant. It is thought that the friction coefficient increased.

As is clear from the above description, an ion comprising a Bronsted acid and a Bronsted base having a linear hydrocarbon group having at least 10 carbon atoms, the difference in pKa (ΔpKa) of which is 6 or more. A lubricant containing a liquid can maintain excellent lubricity even under high-temperature storage conditions, and can maintain its CSS lubricity over a long period of time.
Next, an example applied to a magnetic tape is shown.

(Example 50)
Using the lubricant containing the ionic liquid 12, the magnetic tape described above was produced. As shown in Table 24, the coefficient of friction of the magnetic tape after 100 shuttle runs was 0.19 in an environment at a temperature of −5 ° C. and 0.23 in an environment at a temperature of 40 ° C. and a relative humidity of 90%. there were. The still durability test was more than 60 minutes in an environment at a temperature of −5 ° C., and more than 60 minutes in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. Further, the still durability test after the heating test was more than 60 min in an environment at a temperature of −5 ° C., and more than 60 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test after the heating test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the ionic liquid 12 has excellent friction characteristics, still durability, and shuttle durability.

(Example 51)
Using the lubricant containing the ionic liquid 13, the magnetic tape described above was produced. As shown in Table 24, the coefficient of friction of the magnetic tape after 100 shuttle runs is 0.20 in an environment at a temperature of −5 ° C. and 0.22 in an environment at a temperature of 40 ° C. and a relative humidity of 90%. there were. The still durability test was more than 60 minutes in an environment at a temperature of −5 ° C., and more than 60 minutes in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. Further, the still durability test after the heating test was more than 60 min in an environment at a temperature of −5 ° C., and more than 60 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test after the heating test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the ionic liquid 13 has excellent friction characteristics, still durability, and shuttle durability.

(Example 52)
Using the lubricant containing the ionic liquid 14, the magnetic tape described above was produced. As shown in Table 24, the coefficient of friction of the magnetic tape after 100 shuttle runs was 0.21 in an environment at a temperature of −5 ° C., and 0.24 in an environment at a temperature of 40 ° C. and a relative humidity of 90%. there were. The still durability test was more than 60 minutes in an environment at a temperature of −5 ° C., and more than 60 minutes in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. Further, the still durability test after the heating test was more than 60 min in an environment at a temperature of −5 ° C., and more than 60 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test after the heating test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the ionic liquid 14 has excellent friction characteristics, still durability, and shuttle durability.

(Example 53)
Using the lubricant containing the ionic liquid 15, the magnetic tape described above was produced. As shown in Table 24, the coefficient of friction of the magnetic tape after 100 shuttle runs was 0.22 in an environment at a temperature of −5 ° C., and 0.26 in an environment at a temperature of 40 ° C. and a relative humidity of 90%. there were. The still durability test was more than 60 minutes in an environment at a temperature of −5 ° C., and more than 60 minutes in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. Further, the still durability test after the heating test was more than 60 min in an environment at a temperature of −5 ° C., and more than 60 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test after the heating test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the ionic liquid 15 has excellent friction characteristics, still durability, and shuttle durability.

(Example 54)
Using the lubricant containing the ionic liquid 16, the magnetic tape described above was produced. As shown in Table 24, the coefficient of friction of the magnetic tape after 100 shuttle runs is 0.23 in an environment at a temperature of −5 ° C. and 0.26 in an environment at a temperature of 40 ° C. and a relative humidity of 90%. there were. The still durability test was more than 60 minutes in an environment at a temperature of −5 ° C., and more than 60 minutes in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. Further, the still durability test after the heating test was more than 60 min in an environment at a temperature of −5 ° C., and more than 60 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test after the heating test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the ionic liquid 16 has excellent friction characteristics, still durability, and shuttle durability.

(Example 55)
The magnetic tape described above was produced using a lubricant containing ionic liquid 17. As shown in Table 24, the coefficient of friction of the magnetic tape after 100 shuttle runs was 0.24 in an environment at a temperature of -5 ° C, and 0.28 in an environment at a temperature of 40 ° C and a relative humidity of 90%. there were. The still durability test was more than 60 minutes in an environment at a temperature of −5 ° C., and more than 60 minutes in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. Further, the still durability test after the heating test was more than 60 min in an environment at a temperature of −5 ° C., and more than 60 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test after the heating test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the ionic liquid 17 has excellent friction characteristics, still durability, and shuttle durability.

(Example 56)
Using the lubricant containing the ionic liquid 18, the magnetic tape described above was produced. As shown in Table 24, the coefficient of friction of the magnetic tape after 100 shuttle runs was 0.23 in an environment at a temperature of −5 ° C., and 0.27 in an environment at a temperature of 40 ° C. and a relative humidity of 90%. there were. The still durability test was more than 60 minutes in an environment at a temperature of −5 ° C., and more than 60 minutes in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. Further, the still durability test after the heating test was more than 60 min in an environment at a temperature of −5 ° C., and more than 60 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test after the heating test was more than 200 times in an environment at a temperature of −5 ° C., and more than 200 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the ionic liquid 18 has excellent friction characteristics, still durability, and shuttle durability.

(Comparative Example 31)
Using the lubricant containing the comparative ionic liquid 8, the magnetic tape described above was produced. As shown in Table 24, the coefficient of friction of the magnetic tape after 100 shuttle runs is 0.45 under a temperature of −5 ° C., and 0.49 under a temperature of 40 ° C. and a relative humidity of 90%. there were. The still durability test was 18 min in an environment at a temperature of −5 ° C., and 16 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. In addition, the shuttle durability test was performed 56 times in an environment at a temperature of −5 ° C. and 45 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. Further, the still durability test after the heating test was 14 min in an environment at a temperature of −5 ° C., and 8 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. Further, the shuttle durability test after the heating test was 36 times in an environment at a temperature of −5 ° C., and 30 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the comparative ionic liquid 8 was greatly deteriorated in the still durability and the shuttle durability after the heating test.

(Comparative Example 32)
The magnetic tape described above was produced using a lubricant containing comparative ionic liquid 9. As shown in Table 24, the coefficient of friction of the magnetic tape after 100 shuttle runs is 0.50 in an environment at a temperature of −5 ° C., and 0.55 in an environment at a temperature of 40 ° C. and a relative humidity of 90%. there were. Further, the still durability test was 16 min in an environment at a temperature of −5 ° C., and 14 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. The shuttle durability test was performed 45 times in an environment at a temperature of −5 ° C. and 36 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. Further, the still durability test after the heating test was 12 min in an environment at a temperature of −5 ° C., and 10 min in an environment at a temperature of 40 ° C. and a relative humidity of 30%. Further, the shuttle durability test after the heating test was 28 times in an environment at a temperature of −5 ° C., and 25 times in an environment at a temperature of 40 ° C. and a relative humidity of 90%. From the above results, it was found that the magnetic tape coated with the comparative ionic liquid 9 was greatly deteriorated in the still durability and the shuttle durability after the heating test.

  An ionic liquid of a Bronsted acid and a Bronsted base containing a linear hydrocarbon group having 10 or more carbon atoms, a ΔpKa of which is a compound having a ΔpKa of 12 or more in water, or a ΔpKa of 6 or more in acetonitrile The magnetic tape coated with the above compound as a lubricant showed excellent wear resistance, still durability, and shuttle durability. However, as shown in the comparative example, the compound having a ΔpKa in water of 12 or more, or a ΔpKa in acetonitrile of 6 or more but not having a linear hydrocarbon chain having 10 or more carbon atoms is the same as in the case of the disk described above. The durability was greatly deteriorated.

  As is clear from the above description, it is composed of a Bronsted acid and a Bronsted base having a linear hydrocarbon group having at least 10 carbon atoms, and the difference in pKa (ΔpKa) is expressed in ΔpKa in water. A lubricant containing an ionic liquid that is 12 or more or 6 or more in ΔpKa in acetonitrile can maintain lubricity even under high temperature conditions, and can maintain lubricity for a long period of time. Therefore, the magnetic recording medium using the lubricant containing the ionic liquid can obtain very excellent running performance, wear resistance, and durability.

DESCRIPTION OF SYMBOLS 11 Substrate 12 Underlayer 13 Magnetic layer 14 Carbon protective layer 15 Lubricant layer 21 Substrate 22 Magnetic layer 23 Carbon protective layer 24 Lubricant layer 25 Backcoat layer

Claims (15)

An ionic liquid formed from a Bronsted acid (HX) and a Bronsted base (B) and having a melting point of 100 ° C. or lower;
The ionic liquid is represented by any one of the following general formula (1), the following general formula (2-1), and the following general formula (3-1),
The Bronsted acid is trifluoromethanesulfonic acid, a compound represented by the following structural formula (A), a compound represented by the following structural formula (B), a compound represented by the following structural formula (C), and the following structure Any of the compounds represented by formula (D),
A lubricant characterized in that the difference between the pKa of the Bronsted acid in water and the pKa of the Bronsted base in water is 12 or more.
In the general formula (1), at least one of R ₁ , R ₂ , R ₃ , and R ₄ is a hydrogen atom, and at least one of R ₁ , R ₂ , R ₃ , and R ₄ has a carbon number. It is a group containing 10 or more linear hydrocarbon groups.
In the general formula (2-1), R ₁₁ represents a linear hydrocarbon group having 10 or more carbon atoms.
In the general formula (3-1), R ₂₁ represents a linear hydrocarbon group having 10 or more carbon atoms.
  The lubricant according to claim 1, wherein an exothermic peak temperature in differential thermal analysis (DTA) measurement of the ionic liquid is 370 ° C or higher.   The lubricant according to claim 1, wherein the hydrocarbon group is an alkyl group. An ionic liquid formed from a Bronsted acid (HX) and a Bronsted base (B) and having a melting point of 100 ° C. or lower;
The ionic liquid is represented by any one of the following general formula (1), the following general formula (2-1), and the following general formula (3-1),
The Bronsted acid is trifluoromethanesulfonic acid, a compound represented by the following structural formula (A), a compound represented by the following structural formula (B), a compound represented by the following structural formula (C), and the following structure Any of the compounds represented by formula (D),
The lubricant characterized by the difference between the pKa of the Bronsted acid in acetonitrile and the pKa of the Bronsted base in acetonitrile being 6 or more.
In the general formula (1), at least one of R ₁ , R ₂ , R ₃ , and R ₄ is a hydrogen atom, and at least one of R ₁ , R ₂ , R ₃ , and R ₄ has a carbon number. It is a group containing 10 or more linear hydrocarbon groups.
In the general formula (2-1), R ₁₁ represents a linear hydrocarbon group having 10 or more carbon atoms.
In the general formula (3-1), R ₂₁ represents a linear hydrocarbon group having 10 or more carbon atoms.
  The lubricant according to claim 4, wherein an exothermic peak temperature in differential thermal analysis (DTA) measurement of the ionic liquid is 370 ° C or higher. Containing an ionic liquid formed from Bronsted acid (HX) and Bronsted base (B),
A lubricant characterized in that the ionic liquid is represented by the following structural formula.
In a magnetic recording medium having at least a magnetic layer on a nonmagnetic support,
A magnetic recording medium having the lubricant according to claim 1 in the magnetic layer. Formed from Bronsted acid (HX) and Bronsted base (B),
It is represented by any of the following general formula (1), the following general formula (2-1), and the following general formula (3-1),
The Bronsted acid is trifluoromethanesulfonic acid, a compound represented by the following structural formula (A), a compound represented by the following structural formula (B), a compound represented by the following structural formula (C), and the following structure Any of the compounds represented by formula (D),
The difference between the pKa of the Bronsted acid in water and the pKa of the Bronsted base in water is 12 or more,
An ionic liquid having a melting point of 100 ° C. or lower.
In the general formula (1), at least one of R ₁ , R ₂ , R ₃ , and R ₄ is a hydrogen atom, and at least one of R ₁ , R ₂ , R ₃ , and R ₄ has a carbon number. It is a group containing 10 or more linear hydrocarbon groups.
In the general formula (2-1), R ₁₁ represents a linear hydrocarbon group having 10 or more carbon atoms.
In the general formula (3-1), R ₂₁ represents a linear hydrocarbon group having 10 or more carbon atoms.
  The ionic liquid according to claim 8 whose exothermic peak temperature in differential thermal analysis (DTA) measurement is 370 ° C or more.   The ionic liquid according to claim 8, wherein the hydrocarbon group is an alkyl group. The Bronsted base is, octadecylamine _{(C 18 H 37 NH 2)} , decylamine _{(C 10 H 21 NH 2)} , tetradecyl amine _{(C 14 H 29 NH 2)} , eicosyl amine _{(C 20} H 41 _NH 2) Oleylamine (C ₁₈ H ₃₅ NH ₂ ), 2-heptylundecylamine (CH ₃ (CH ₂ ) ₉ CH (C ₇ H ₁₅ ) NH ₂ ), and any of the compounds represented by the following structural formula (1) The ionic liquid according to claim 8, wherein the ionic liquid is one of these.
Formed from Bronsted acid (HX) and Bronsted base (B),
It is represented by any of the following general formula (1), the following general formula (2-1), and the following general formula (3-1),
The Bronsted acid is trifluoromethanesulfonic acid, a compound represented by the following structural formula (A), a compound represented by the following structural formula (B), a compound represented by the following structural formula (C), and the following structure Any of the compounds represented by formula (D),
The difference between the pKa of the Bronsted acid in acetonitrile and the pKa of the Bronsted base in acetonitrile is 6 or more,
An ionic liquid having a melting point of 100 ° C. or lower.
In the general formula (1), at least one of R ₁ , R ₂ , R ₃ , and R ₄ is a hydrogen atom, and at least one of R ₁ , R ₂ , R ₃ , and R ₄ has a carbon number. It is a group containing 10 or more linear hydrocarbon groups.
In the general formula (2-1), R ₁₁ represents a linear hydrocarbon group having 10 or more carbon atoms.
In the general formula (3-1), R ₂₁ represents a linear hydrocarbon group having 10 or more carbon atoms.
  The ionic liquid according to claim 12 whose exothermic peak temperature in differential thermal analysis (DTA) measurement is 370 ° C or more. The Bronsted base is, octadecylamine _{(C 18 H 37 NH 2)} , decylamine _{(C 10 H 21 NH 2)} , tetradecyl amine _{(C 14 H 29 NH 2)} , eicosyl amine _{(C 20} H 41 _NH 2) Oleylamine (C ₁₈ H ₃₅ NH ₂ ), 2-heptylundecylamine (CH ₃ (CH ₂ ) ₉ CH (C ₇ H ₁₅ ) NH ₂ ), a compound represented by the following structural formula (2), and The ionic liquid according to any one of claims 12 to 13, which is any one of the compounds represented by the structural formula (3).
An ionic liquid formed from a Bronsted acid (HX) and a Bronsted base (B) and represented by the following structural formula.